Abstract: The 2D/1D transport method is widely implemented for direct whole-core transport calculation because of its good balance between efficiency and accuracy. In the 2D/1D transport method, negative total source may occur for method of characteristics (MOC) calculation in iteration process, which will lead to iteration divergence. The negative total source in the MOC equation was studied and the improved leakage splitting method was proposed to improve stability for 2D/1D transport method in this paper. With the new method, the accuracy is preserved while the memory cost only increases slightly. High leakage case and the C5G7 and VERA-3A benchmarks were tested to show the accuracy and performance of the proposed method.