Objective? To analyze the relationship between systemic immune-inflammation index (SII) or platelet to lymphocyte ratio (PLR) and postoperative prognosis of patients with gastric cancer, provide reference for clinical evaluation of patients' prognosis. Methods The retrospective analysis of the clinical data of 106 patients with gastric cancer who treated with surgical treatment in Nantong Tumor Hospital from January 2015 to December 2016 was conducted, the patients were divided into the good prognosis group (in survival, 45 cases) and the poor prognosis group (in death, 61 cases) according to their 5-year survival, the platelet count, neutrophil count and lymphocyte count were detected, and the SII level, PLR ratio were calculated. According to the level of SII, they were divided into the SII high expression group (SII ≥412.30, 48 cases) and the SII low expression group (SII<412.30, 58 cases); according to the level of PLR ratio, they were divided into the high expression group of PLR (PLR≥125, 39 cases) and the low expression group of PLR (PLR<125, 67 cases). The relationship between the clinical characteristics of gastric cancer patients and preoperative SII or PLR levels were analysed; the clinical characteristics of patients in the good prognosis group and the poor prognosis group were counted; the influencing factors of postoperative prognosis of gastric cancer patients was analysed by the COX regression model. Results The proportion of patients with the largest diameter of tumor ≥4 cm, T stage T3+T4, distant metastasis, subgastric tumor, the degree of differentiation with low differentiation, carcinoembryonic antigen (CEA) >5 ng/mL, carbohydrate antigen 199 (CA199)≥37 U/mL in the SII high expression group and the high expression group of PLR were significantly higher than those in the SII low expression group and the low expression group of PLR, respectively; the proportion of patients with age ≥60 years, the largest diameter of tumor ≥4 cm, T stage T3+T4, distant metastasis, subgastric tumor, the degree of differentiation with low differentiation,CEA>5 ng/mL, CA199≥37 U/mL, SII ≥412.30, PLR ratio ≥125 in the good prognosis group were significantly lower than those in the poor prognosis group; the result of the COX regression model analysis showed that, age ≥60 years, maximum tumor diameter ≥4 cm, T stage T3+T4, distant metastasis, subgastric tumor, the degree of differentiation with low differentiation, CEA>5 ng/mL, CA199 ≥37 U/mL, SII ≥412.30, PLR≥125 were all the independent risk factors for postoperative prognosis of gastric cancer patients (HR=1.451, 1.356, 2.451, 1.549, 1.285, 1.196, 1.795, 1.426, 1.356, 1.245, all P<0.05). Conclusion SII and PLR levels are closely related to the postoperative prognosis of patients with gastric cancer, high expression of SII and PLR are the independent risk factor for the postoperative prognosis of patients with gastric cancer, early monitoring of SII and PLR levels is helpful to evaluate the postoperative prognosis of patients with gastric cancer.