BACKGROUND: Immunotherapy combined with chemotherapy has emerged as the first-line standard treatment for advanced gastric cancer. However, obvious survival benefits in patients with peritoneal metastatic gastric cancer remain elusive. The combination of anti-angiogenic agents and immunotherapy has shown synergistic effects. However, currently there are no relevant reports on the efficacy and safety of immunotherapy combined with anti-angiogenic agents and chemotherapy in patients with gastric cancer peritoneal metastatic. METHODS: We conducted a multicenter, retrospective clinical study in four independent healthcare facilities, enrolling advanced gastric cancer patients with peritoneal metastatic who received immunotherapy in combination with anti-angiogenic agents and chemotherapy between January 2020 and March 2023. All patients were treated with triple combination regimen for at least two and up to eight cycles before being adjusted for immunotherapy and targeted therapy. This study observed overall survival (OS) and time to treatment failure (TTF), as well as an exploratory analysis of the impact of ascites and peritoneal metastases on the prognosis of all patients. RESULTS: This study enrolled 30 eligible patients in the final analysis cohort. The median TTF and OS were 7.03 months [95% confidence interval (CI), 4.17-9.89] and 13.33 months (95% CI: 10.96-15.71), respectively. The 6-month and 12-month OS rates were 83.0% and 53.0%, respectively. The objective response rate (ORR) was 58.3%, and the disease control rate (DCR) was 83.3% in 12 patients who were evaluated for response with at least one measurable lesion. Exploratory subgroup analysis revealed that the median TTF and OS in the subgroup without ascites were significantly better than those in the subgroup with ascites, with a median TTF of 9.03 vs. 4.63 months (χ = 8.579, P = 0.003), and median OS of 17.83 vs. 11.87 months (χ = 6.155, P = 0.013). Conversely, the extent of peritoneal metastasis had little effect on TTF and OS. The common adverse reactions were leukopenia (46.67%), neutropenia (43.33%), fatigue (36.67%), anemia (36.67%), decreased appetite (36.67%), thrombocytopenia (33.33%), and hypertension (33.33%). No new safety signals were observed. CONCLUSIONS: The combination of immunotherapy, anti-angiogenic agents, and chemotherapy demonstrated therapeutic potential with a manageable safety profile in patients with peritoneal metastatic gastric cancer. These findings should be interpreted cautiously due to the inherent limitations of retrospective analyses and need to be validated through prospective randomized controlled trials to establish clinical efficacy and optimize patient selection criteria.