To evaluate the effect of thymopentin (TP5) on immune function and curative effect in adjuvant therapy for patients with lung cancer, we searched online for randomized, placebo-controlled trials that using TP5 as an adjuvant therapy with chemotherapy or radiotherapy for patients with lung cancer, and then evaluated the trials that meet criteria with the software RevMan5.3. As a result, 9 trials were included and 784 patients were observed. The meta-analysis shows that there is no significant change between the experimental group and the control group in terms of the curative effect of lung cancer (OR＝1.44, 95%CI(0.99, 2.10), P＝0.06＞0.05). As to the effect of immune function, TP5 altered the CD3＋cell level (OR＝5.88, 95% CI(2.34, 9.42), P＝0.001, CD4＋ cell level(OR＝8.32, 95%CI(5.22, 11.42), P＜0.00001), but did not alter the CD8＋ cell level (OR＝－3.12, 95% CI(－9.02, 2.79), P＞0.05) which led to a significant change of the CD4＋/CD8＋ ratio(OR＝0.38, 95% CI(0.18, 0.59), P＝0.0002). To sum up, TP5 altered the CD3＋ cell level, CD4＋ cell level and CD4＋/CD8＋ ratio but did not alter the CD3＋ cell level and curative effect.