Compared with other anti-tumor drugs, immune checkpoint inhibitors (ICIs) have their own unique pharmacokinetics (PK) and pharmacodynamics (PD), and affect patient clinical outcomes. However, at present, the data on the PK and PD characteristics of ICIs in the Chinese population are still lacking, thus further clinical trials are needed to verify them. At the same time, a large proportion of patients have no response to ICIs or the efficacy is poor, and even bring greater side effects, so it is particularly important to find effective biomarkers to predict the efficacy and adverse reactions of patients with ICIs treatment.The purpose of this study is to explore the correlation between blood concentration of Sintilimab and related predictors with efficacy and adverse reactions in patients with advanced gastric cancer so as to provide clinical reference for individualized treatment of patients with gastric cancer.