Background: Peritoneal metastasis is the most common metastatic mode of advanced gastric cancer, which is prone to poor prognosis and is also one of the common causes of death in patients with distant gastric cancer metastasis.The purpose of this paper was to establish a new hematologic scoring (an NPD scoring) by the neutrophil-lymphocyte ratio (NLR) and platelet- lymphocyte ratio (PLR) A and D-dimer (DDI), and its association with the peritoneal cancer index (PCI) was evaluated, and the ability of NPD scoring system to judge the prognosis of peritoneal metastasis of gastric cancer. Methods: This was a single-center, nonrandomized, retrospective, cohort study.102 patients with peritoneal metastasis of gastric cancer who underwent diagnostic staging laparoscopy (DSL) were enrolled and assessed with PCI scores.. According to the first PCI (PCI < 15), the patients were divided into low PCI group (n = 67) and high PCI group (n = 35). Through univariate analysis and multivariate analysis, it was found that NLR, PLR and DDI were related to high PCI (≥ 15), and NPD scoring system was established. Chi-square test was used to evaluate the relationship between NPD score, PCI and prognosis. Results: The cohort study found that the differences of NLR, PLR and DDI between low PCI group (n = 67) and high PCI group (n = 35) were statistically significant (P < 0.05). Univariate and multivariate analysis showed that NLR, PLR and DDI were independent risk factors for high PCI (P < 0.05). The NPD score of patients in the high PCI group was significantly higher than those in the low PCI group (P = 0.001). The survival rate of patients in high-risk group (NPD ≥ 2 points) was significantly lower than that in low-risk group (NPD < 2 points) (P = 0.003). Multivariate analysis showed that PCI and NPD score ≥ - 2 were independent predictors of OS. Conclusions: NPD score can be used as a blood marker to predict PCI and prognosis in patients with peritoneal metastasis of gastric cancer, and to guide clinical treatment. This new scoring system is an economic and convenient tool for predicting PCI and judge the prognosis of peritoneal metastasis.