【Abstract】 Objective To explore the efficacy of gefitinib combined with gemcitabine + cisplatin (GP) chemotherapy in the treatment of non small cell lung cancer. Methods Seventy patients with advanced NSCLC were selected and randomly divided into control group and observation group according to the random number table, with 35 cases in each group. The control group was treated with gefitinib. The observation group was treated with GP regimen on the basis of the control group. 21d was 1 course of treatment, and both groups were treated for 2 courses. To evaluate the clinical efficacy of the two groups, and compare the immune function indexes (CD4+, CD8+, CD4+/CD8+, IgA, IgG, IgM), lung function indexes (FEV1, FVC, FEV1/FVC), tumor markers (CYFRA21-1, CEA) changes in levels and occurrence of adverse reactions. Results The overall clinical efficacy of the observation group was significantly better than that of the control group (P＜0.05). The ORR and DCR of the observation group were higher than those of the control group, but the difference between the two groups was not statistically significant (all P＞0.05). Before treatment, there was no statistically significant difference in the above indicators between the two groups (all P＞0.05). After treatment, the observation group CD8+, CYFRA21-1, CEA were significantly lower than the control group, CD4+, CD4+/CD8+, IgA, IgG, IgM, FEV1, FEV1/FVC were significantly higher than the control group, and the differences were statistically significant ( All P＜0.05). There was no significant difference in the incidence of adverse reactions such as skin adverse reactions, diarrhea, nausea and vomiting, abnormal liver function between the two groups (P＞0.05). Conclusion Gefitinib combined with GP in the treatment of advanced NSCLC can improve the overall clinical efficacy, and can effectively reduce the level of tumor markers, improve immune function and lung function, and have a lower incidence of adverse reactions.