Objective To study the metastatic lymph node ratio for grouping of gastric cancer patients and evaluate the prognosis. Methods A total of 392 patients of gastric cancer who underwent radical gastrectomy with stage Ⅱ-Ⅲ according to the American Joint Committee on Cancer (AJCC) 8th in Zhongshan Hospital of Fudan University from January 2004 to July 2018 were retrospectively analyzed. X-tile software was used to group patients based on the metastatic lymph node ratio. The correlation between metastatic lymph node ratio and other clinicopathological factors was made, and the evaluation of prognosis of patients was assessed. The nomogram model of prediction was established. Calibration curves were drawn, and comparison between the curves and data of patients was performed. Internal validation was done by the Bootstrap method. Concordance index (C-index) was calculated to test the accuracy of model. Results X-tile analysis showed that the best cut-off values were 0.20 (20%) and 0.70 (70%) of metastatic lymph node ratio. According to the cut-off values, the patients in this study were divided into 3 subgroups at metastatic lymph node ratio 1(0-20%), metastatic lymph node ratio 2 (21%-69%), and metastatic lymph node ratio 3 (70%-100%) with significant difference in survival statistically(P<0.001). Univariate analysis showed that metastatic lymph node ratio, TNM stage, T stage, N stage, lymphatic invasion, and age were related factors affecting prognosis. Multivariate analysis showed that metastatic lymph node ratio, T stage, N stage, lymphatic invasion, and age were independent factors affecting prognosis. Receiver operator characteristic curve of postoperative overall survival rates of patients were drawn using metastatic lymph node ratio, TNM stage, lympha-tic invasion and age, of which area under the curve were 0.699, 0.667, 0.587 and 0.561. The independent 4 risk factors were taken into account to construct nomogram prediction models. C-index was 0.707 (95% CI: 0.705-0.708). The 1-, 3- and 5- year survival rate predicted by the nomogram were consistent with the actual data. Conclusions Metastatic lymph node ratio is an independent factor affecting the prognosis of radical gastrectomy for stage Ⅱ-Ⅲ gastric cancer. Metastatic lymph node ratio is an effective supplement to pathological N stage, which can direct reasonable treatment.