Objective：To investigate the abnormalities in routine blood parameters among gastric cancer patients and analyze their trends over the course of the disease. Methods：This study included the population who participated in the Taihu Tumour Biomarkers Biobank（TBTB）in Wuxi from August 2020 to December 2021，with 1 920 cases who already had gastric cancer at baseline as the gastric cancer group and 7 680 cancer-free cases matched 1∶4 for age and sex as the healthy control group. A study design was adopted to explore the association between routine blood tests and the prevalence of gastric cancer using multiple linear regression model，and the Kruskal -Wallis H test was further used to compare the differences in routine blood tests across different stages of the disease between groups. Results：Multiple linear regression model showed that levels of hemoglobin（HGB），platelet count（PLT），red blood cell count（RBC），white blood cell count（WBC），mean hemoglobin content（MCH）and mean corpuscular hemoglobin concentration （MCHC）were lower in gastric cancer patients than in controls，with HGB levels decreasing the most（β=-0.78，95% CI：-0.83--0.73， P ＜ 0.001），and red blood cell volume distribution width（RDW）（β=0.13，95% CI：0.08-0.17，P ＜ 0.001）and hematocrit（HCT）（β= 0.16，95% CI：0.10-0.22，P ＜ 0.001）levels were higher than those of the control group，suggesting that anemia-related signs were more common in gastric cancer patients. We found that WBC level showed a gradual decreasing trend during the disease progression in gastric cancer patients（P ＜ 0.001），and HGB，RBC and hematocrit（HCT）levels tended to increase with the duration of gastric cancer （all P ＜ 0.001），but they were still lower than those of the control group. Conclusion：This study indicates that gastric cancer patients are more likely to exhibit anemia - related abnormalities compared with healthy individuals. Additionally，certain blood routine parameters show significant changing trends with disease progression，providing valuable insights for clinical monitoring and management of gastric cancer.