Abstract: Objective By comparing the differences of lymphocyte subsets and VEGF levels before and after DC-CIK treatment and intrathracic chemotherapy of MPE(malignant pleural effusion)，we try to discover the possible therapeutic mechanism. Methods The changes of lymphocyte subsets and VEGF levels were detected by FCM and ELISA respectively before and after the different treatments. Results （1）DC-CIK group，the percentage of CD3-CD16+CD56+NK cells，CD3+CD16+CD56+T cells and CD8+CD28+T cells were significantly increased(P＜0.05) and the level of VEGF was slightly decreased(P>0.05)in the fluids of post-treatment.（2） Chemotherapy group，the percentage of CD3+T cells，CD3+CD4+T cells and CD4+CD25+T cells as well as the level of VEGF are significantly decreased(P<0.05). Conclusion （1）The possible mechanism of DC-CIK transfusion is to enhance the local immune function;（2）Besides killing the tumor cell directly，the possible mechanisms of intrathoracic chemotherapy involves in improving the local immune suppression and lowering VEGF level.