Although recent advances in systemic chemotherapy have improved the clinical outcomes of gastric cancer patients with peritoneal metastasis, the peritoneum still represents a common site of treatment failure and disease recurrence. Neoadjuvant intraperitoneal–systemic chemotherapy has been acknowledged as a more aggressive treatment for gastric cancer patients with peritoneal metastasis. In this multicenter phase III randomized controlled trial, 238 patients will be randomly separated into two groups in a 2:1 ratio after laparoscopic exploration. The experimental arm will receive the proposed neoadjuvant intraperitoneal–systemic chemotherapy regimen, whereas the control group will receive a Paclitaxel + S-1 (PS) chemotherapy regimen. The endpoints for the study are overall survival, response rate, gastrectomy radicality rate, progression-free survival and adverse events.