Objective To investigate the efficacy and safety of neoadjuvant intraperitoneal and systemic chemotherapy （NIPS） combined with sintilimab in the treatment of peritoneal metastasis of gastric cancer. Methods A total of 82 patients with gastric cancer peritoneal metastasis admitted from June 2021 to June 2024 were selected and divided into a control group and an observation group according to treatment methods, with 41 cases in each group. The control group was treated with NIPS therapy, while the observation group was treated with NIPS combined with sintilimab. Clinical efficacy, tumor markers carbohydrate antigen （CA） 125, CA19-9, and carcinoembryonic antigen （CEA）, cytokine levels vascular endothelial growth factor （VEGF）, 6-month survival, and toxic side effects were compared between the two groups. Results The clinical effective rate of the observation group （70.73%, 29/41） was higher than that of the control group （48.78%, 20/41） （P<0.05）. The levels of CA125, CA19-9, CEA, and VEGF were not different between the two groups before treatment; the levels were reduced after 3 months of treatment, and lower in the observation group than in the control group （P<0.05）. During the 6-month follow-up period, compared to the control group （41.46%, 17/41）, the observation group had a higher rate of survival （65.85%, 27/41） （P<0.05）. There was no statistically significant difference in toxic side effects between the two groups （P>0.05）. Conclusion The combination of NIPS and sintilimab has shown high efficacy and good safety in the treatment of gastric cancer peritoneal metastasis, providing a new choice for the treatment of patients with gastric cancer peritoneal metastasis.