diff --git a/fluss-client/src/main/java/org/apache/fluss/client/write/RecordAccumulator.java b/fluss-client/src/main/java/org/apache/fluss/client/write/RecordAccumulator.java
index 9e08e1a95d..80f9b75d17 100644
--- a/fluss-client/src/main/java/org/apache/fluss/client/write/RecordAccumulator.java
+++ b/fluss-client/src/main/java/org/apache/fluss/client/write/RecordAccumulator.java
@@ -59,6 +59,7 @@
 import java.util.Optional;
 import java.util.Set;
 import java.util.concurrent.ConcurrentMap;
+import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
 
 import static org.apache.fluss.record.LogRecordBatchFormat.NO_BATCH_SEQUENCE;
@@ -103,6 +104,9 @@ public final class RecordAccumulator {
     /** The chunked allocation manager factory, stored for explicit native memory release. */
     private final ChunkedAllocationManager.ChunkedFactory chunkedFactory;
 
+    /** Guard to make {@link #destroyResources()} idempotent. */
+    private final AtomicBoolean resourcesDestroyed = new AtomicBoolean(false);
+
     /** The pool of lazily created arrow {@link ArrowWriter}s for arrow log write batch. */
     private final ArrowWriterPool arrowWriterPool;
 
@@ -960,16 +964,29 @@ public ReadyCheckResult(
         }
     }
 
-    /** Close this accumulator and force all the record buffers to be drained. */
+    /** Close this accumulator to reject new appends. */
     public void close() {
         closed = true;
+    }
 
+    /**
+     * Destroy all resources held by this accumulator including the Arrow writer pool and buffer
+     * allocator.
+     *
+     * <p>This must only be called after the sender thread has fully exited and no more drain
+     * operations will occur. Otherwise, draining batches may attempt to recycle Arrow writers using
+     * an already-closed allocator, causing "Accounted size went negative" errors.
+     *
+     * <p>This method is idempotent: subsequent calls after the first are no-ops.
+     */
+    @VisibleForTesting
+    public void destroyResources() {
+        if (!resourcesDestroyed.compareAndSet(false, true)) {
+            return;
+        }
         writerBufferPool.close();
         arrowWriterPool.close();
-        // Release all the memory segments.
-        bufferAllocator.releaseBytes(bufferAllocator.getAllocatedMemory());
         bufferAllocator.close();
-        // Release native memory held by the chunked allocation manager factory.
         chunkedFactory.close();
     }
 
diff --git a/fluss-client/src/main/java/org/apache/fluss/client/write/Sender.java b/fluss-client/src/main/java/org/apache/fluss/client/write/Sender.java
index 5fc5ba2746..7b456d4bd9 100644
--- a/fluss-client/src/main/java/org/apache/fluss/client/write/Sender.java
+++ b/fluss-client/src/main/java/org/apache/fluss/client/write/Sender.java
@@ -167,6 +167,8 @@ public void run() {
             }
         }
 
+        destroyResources();
+
         // TODO if force close failed, add logic to abort incomplete batches.
         LOG.debug("Shutdown of Fluss write sender I/O thread has completed.");
     }
@@ -643,4 +645,18 @@ public void initiateClose() {
         accumulator.close();
         running = false;
     }
+
+    /**
+     * Releases all resources held by the accumulator (Arrow writer pool, buffer allocator, etc.).
+     *
+     * <p>In production, this is called at the end of {@link #run()} after both the main loop and
+     * the shutdown drain loop have completed, so no further drain operations will touch the Arrow
+     * allocator.
+     *
+     * <p>This method is idempotent: repeated calls are harmless because the underlying {@link
+     * RecordAccumulator#destroyResources()} tolerates multiple invocations.
+     */
+    void destroyResources() {
+        accumulator.destroyResources();
+    }
 }
diff --git a/fluss-client/src/test/java/org/apache/fluss/client/write/SenderTest.java b/fluss-client/src/test/java/org/apache/fluss/client/write/SenderTest.java
index cd59e8bdfc..2c4d30e96a 100644
--- a/fluss-client/src/test/java/org/apache/fluss/client/write/SenderTest.java
+++ b/fluss-client/src/test/java/org/apache/fluss/client/write/SenderTest.java
@@ -43,6 +43,7 @@
 import org.apache.fluss.server.tablet.TestTabletServerGateway;
 import org.apache.fluss.utils.clock.SystemClock;
 
+import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
@@ -101,6 +102,11 @@ public void setup() {
         sender = setupWithIdempotenceState();
     }
 
+    @AfterEach
+    public void teardown() throws Exception {
+        sender.destroyResources();
+    }
+
     @Test
     void testSimple() throws Exception {
         long offset = 0;
@@ -171,6 +177,39 @@ void testInitWriterIdRequest() throws Exception {
         assertThat(idempotenceManager.writerId()).isEqualTo(0L);
     }
 
+    /**
+     * Verifies the two-phase close prevents the shutdown race condition. Previously,
+     * initiateClose() destroyed the Arrow BufferAllocator while the sender's drain loop was still
+     * running, causing "Accounted size went negative". With the fix, initiateClose() only rejects
+     * new appends; resource destruction is deferred to destroyResources().
+     */
+    @Test
+    void testCloseSenderBeforeAccumulatorDrain() throws Exception {
+        // Append a record so there is an undrained batch.
+        appendToAccumulator(tb1, row(1, "a"), (tb, leo, e) -> {});
+
+        // Sender begins to prepare write data.
+        Cluster clusterSnapshot = metadataUpdater.getCluster();
+        RecordAccumulator.ReadyCheckResult readyCheckResult = accumulator.ready(clusterSnapshot);
+        assertThat(readyCheckResult.readyNodes).isNotEmpty();
+
+        // Close the accumulator before it drains — this is the race window.
+        sender.initiateClose();
+
+        // Drain after the sender is closed. Before the fix this threw "Accounted size went
+        // negative" because the Arrow
+        // allocator was closed while the drain was still running.
+        Map<Integer, List<ReadyWriteBatch>> drained =
+                accumulator.drain(clusterSnapshot, readyCheckResult.readyNodes, MAX_REQUEST_SIZE);
+        assertThat(drained).isNotEmpty();
+        sender.runOnce();
+        assertThat(accumulator.hasUnDrained()).isFalse();
+
+        // even double destroy is still safe.
+        sender.destroyResources();
+        sender.destroyResources();
+    }
+
     @Test
     void testCanRetryWithoutIdempotence() throws Exception {
         // do a successful retry.