〔Abstract〕 Objective To investigate the relationship between the expression of thymidine synthase(TS) in gastric cancer and clinicopathological factors, survival and prognosis, as well as the relationship between the blood TS concentration and the timing of intraperitoneal administration of raltitrexed in patients with gastric cancer. Methods Immunohistochemistry was used to detect TS expression in 80 cases of gastric cancer and adjacent tissues. Enzyme-linked immunosorbent assay(ELISA) was used to determine the concentration of TS in 20 cases of fresh gastric cancer and paracancer tissues, and the concentration of TS in blood before and after intraperitoneal administration of raltitrexed in 40 cases. q-PCR was used to detect TS mRNA expression in 20 cases of fresh frozen gastric cancer and its adjacent tissues. Intraperitoneal chemotherapy: Abdominal puncture was given to the group 2 d before surgery, and before abdominal closure was given to the group after surgery. Results The positive rate of TS in 80 gastric cancer tissues(48.75%, 39/80) was higher than that in the adjacent tissues(23.75%, 19/80), and the difference was statistically significant(P<0.001).The average TS concentration in the fresh gastric cancer tissues(1.105×10-3±0.177×10-3)μmol/L was significantly higher than that in the adjacent gastric tissues(0.811×10-3±0.192×10-3)μmol/L, and the difference was statistically significant(P<0.001). TS mRNA expression in 20 fresh gastric cancer tissues(3.08±1.70) was higher than that in adjacent gastric tissues(1.02±0.23), and the difference was statistically significant(P<0.001). The expression of TS in gastric cancer tissue was correlated with the degree of tumor differentiation(P<0.05), and the expression of TS in blood was correlated with N stage and the degree of tumor differentiation(P<0.05). The survival rate of patients with TS negative gastric cancer was higher than that of patients with TS positive gastric cancer(P<0.001), and TS was also an independent risk factor for the prognosis of gastric cancer. After intraperitoneal administration of raltitrexed, the blood TS concentration dropped to the lowest value on the second day, and the disease-free survival rate of the group two days before surgery was higher than that of the group after surgery(P<0.05). Conclusion The positive expression rate of TS increases in gastric cancer, and its expression is related to the degree of tumor differentiation and survival prognosis of patients. Changes in blood TS concentration after intraperitoneal administration of Retictrexate in patients with gastric cancer can be used to predict the optimal time for intraperitoneal administration, and the optimal time for intraperitoneal administration of retictrexate is two days before surgery.