Objective To study the predictive value of systemic immune⁃inflammation index（SII）in the immune therapy of non⁃small cell lung cancer（NSCLC）patients. Methods The clinical data of 88 patients with NSCLC who received immunotherapy in our hospital from January 2019 to December 2019 were selected. The time⁃ dependent receiver operating curve was used to determine the optimal cut⁃off value of SII. The clinical therapeutic effects of the two groups and their relationship of SII with clinicopathological characteristics were statistically analyzed. Kaplan⁃Meier survival analysis（Log⁃Rank test）were used to analyze the difference in survival prognosis of patients with different SII levels. Univariate and multivariate COX regression analysis were used to analyze risk factors affecting the survival prognosis of NSCLC patients receiving immunotherapy. Results The best cut⁃off value of SII was 423. SII was related to the clinical stage of NSCLC patients（all P < 0.05）. The disease control rate in the high SII group was 23.26%（10/43），which was significantly lower than 53.33%（24/45）in the low SII group （χ2 = 8.390，P = 0.004）. The 3⁃year overall survival rate of the high SII group was 18.60%（8/43），which was sig⁃ nificantly lower than that of the low SII group，51.11%（23/45）（Log ⁃ rank χ2 = 6.721，P = 0.000）；the median overall survival of the high SII group was was 16.25（9.20 ~ 19.36）months，which was significantly lower than 22.23（14.57 ~ 26.92）months in the low SII group（U = 4.886，P = 0.000）. Tumor stage IV（HR = 1.637，95%CI： 1.054 ~ 2.269，P = 0.030），high expression of SII（HR = 1.854，95%CI：1.120 ~ 2.568，P = 0.009）were inde⁃ pendent risk factors affecting the survival prognosis of NSCLC patients. Conclusion SII is an independent factor predicting the prognosis of NSCLC patients after immunotherapy. The detection of SII before immunotherapy in NSCLC patients is a new peripheral blood index for prognostic judgment.