Abstract: OBJECTIVE To investigate the factors influencing postoperative pulmonary infection and changes in peripheral blood p38 mitogen-activated protein kinase (p38 MAPK) signal, carbohydrate antigen 153 (CA153), and circulating tumor cells (CTCs) in patients with gastric cancer. METHODS A total of 98 patients with gastric cancer undergoing radical resection in General Surgery Department of Chongqing Emergency Medical Center between Jan. 2016 and Jan. 2021 were selected, and were divided into 21 cases of the infection group and 77 cases of the non-infection group according to presence or absence of pulmonary infection within 1 month after surgery. The clinical characteristics such as gender and age in both groups were recorded. The level of serum CA153 was detected by electrochemiluminescence. The positive expression rate of peripheral blood CTCs was detected by Cell Search system. The expression levels of p38 MAPK, extracellular regulated protein kinases 1/2 (ERK1/2), c-Jun N-terminal kinase (JNK), p-p38 MAPK, p-ERK1/2 and p-JNK proteins were detected by Western blot. The influencing factors of postoperative pulmonary infection in gastric cancer were analyzed by binary Logistic regression analysis. RESULTS The main pathogens of pulmonary infection after gastric cancer surgery were mainly Gram-negative bacteria (59.38%). The level of serum CA153, positive expression rate of CTCs and expression levels of p-p38 MAPK, p-ERK1/2 and p-JNK proteins in the infection group were higher than those in non-infection group (P<0.05). Logistic regression analysis showed that smoking history, diabetes mellitus and catheterization time were influencing factors of postoperative pulmonary infection in patients with gastric cancer (P<0.05). CONCLUSION Smoking history, combined diabetes mellitus and long catheterization time were influencing factors of postoperative pulmonary infection in patients with gastric cancer, and the infection caused elevated levels of CA153, CTCs, p-p38 MAPK, p-ERK1/2 and p-JNK proteins in patients.