To evaluate the efficacy of hyperthermic intraperitoneal chemotherapy (HIPEC) combined with systemic therapy in gastric cancer patients with peritoneal metastasis, and analyze its impact on tumor conversion and survival outcomes. Methods    A single-center retrospective study was conducted, enrolling 63 newly diagnosed gastric cancer patients with peritoneal metastasis treated at the Department of Gastric Surgery Ⅱ, Fudan University Shanghai Cancer Hospital, between December 2023 and February 2025. All patients received HIPEC treatment based on taxane drugs. Systemic chemoimmunotherapy was initiated within 2 weeks post-HIPEC, with follow-up assessments every 3 months. Multidisciplinary team evaluations determined eligibility for R0 resection. Primary outcome measures included therapeutic efficacy (disease control rate, objective response rate), R0 resection rate, and overall survival. Results    Among 63 patients ,there were 35 males and 28 females with median age at 55 (range 27-79) years. There were 4 cases in the simple HIPEC group, 7 cases in the HIPEC sequential chemotherapy group, 50 cases in the HIPEC sequential chemotherapy and immunotherapy group, and 2 cases in the HIPEC sequential chemotherapy, immunotherapy, and targeted therapy group. The overall objective response rate of all the patients was 49.2% (31/63), with a disease control rate of 71.4% (45/63). In the HIPEC sequential chemotherapy and immunotherapy group, partial remission was achieved in 26 cases (52.0%), 25.0% in the simple HIPEC group, and 40.0% in the HIPEC sequential chemotherapy group. There was no statistically significant difference between the three groups (P=0.370). By the follow-up cutoff, 14 patients (22.2%) achieved R0 resection criteria. Among them, 11 cases belonged to the HIPEC sequential chemotherapy-immunotherapy combination treatment group. The number of treatment cycles for patients who received R0 resection in the HIPEC sequential chemotherapy-immunotherapy group was significantly higher than that of patients who did not achieve conversion success in the same group, and the difference was statistically significant ［(6.09±1.52) vs. (3.69±1.27), P<0.05］. The cohort’s median survival was 14 months, with all R0 resection patients alive at last follow-up, whereas radiologically progressive patients had a median survival of 6 months. Conclusion    Paclitaxel-based HIPEC improves locoregional tumor burden in gastric cancer patients with peritoneal metastasis. The HIPEC-sequential chemoimmunotherapy strategy may create opportunities for conversion surgery and prolong survival in select patients.