〔Abstract〕 Objective To investigate the expression of human cysteine protease inhibitor S(CST4), Helicobacter pylori(HP) antibody typing and human epidermal growth factor receptor 2(HER2) in patients with gastric cancer and its predictive value for lymph node metastasis and TNM staging of gastric cancer. Methods A total of 150 gastric cancer patients admitted to Chaohu Hospital Affiliated to Anhui Medical University for surgery from December 2021 to December 2023 were selected as the study objects. Serum CST4 and HP antibody typing were performed before surgery, and HER2 expression levels in gastric cancer tissues were detected by immunohistochemistry after surgery. The clinicopathological data of gastric cancer patients with different serum CST4, HP antibody types and HER2 expression were compared and the correlation was analyzed. ROC curve was used to compare the predictive value of single and combined detection of serum CST4, HP antibody typing and HER2 expression in lymph node metastasis and TNM staging of gastric cancer. Results Patients with CST4, HPI and HER2-positive expression had deeper tumor invasion and were more likely to develop distant lymph node metastasis, and TNM stages were more likely to occur in Ⅲ and Ⅳ stages(P<0.05). Meanwhile, patients with CST4 positive expression were more likely to have vascular and nerve invasion(P<0.05). In patients with HPI positive expression, tumors were more likely to occur in the cardia and the bottom of the stomach, and the tumor diameter was larger and vascular invasion was more likely(P<0.05), while HER2 was negatively correlated with the degree of tumor differentiation, and the tumors were more likely to occur in high and secondary differentiation(P<0.05). ROC curve analysis showed that the AUC of single and combined detection of serum CST4, HPI and HER2 expression to predict lymph node metastasis of gastric cancer were 0.780, 0.676, 0.611 and 0.872, respectively(P<0.05). The AUC for TNM stage diagnosis of gastric cancer were 0.762, 0.635, 0.613 and 0.801(P<0.05), respectively. The diagnostic efficiency of combined detection was higher than that of single detection. Conclusion The expression of CST4, HPI and HER2 in serum is closely related to the depth of tumor invasion, lymph node metastasis and TNM stage. The expression of CST4, HPI and HER2 in serum can be used as an important predictor of lymph node metastasis and TNM stage in gastric cancer patients, providing a new idea for clinical diagnosis.