【Abstract】 Objective This cross-sectional study aims 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 1920 cases who already had gastric cancer at baseline as the gastric cancer group and 7680 cancer-free cases matched 1:4 for age and sex as the healthy control group. A cross-sectional survey design was adopted to explore the association between routine blood tests and the prevalence of gastric cancer using multiple linear regression modelling, and the Kruskal-Wallis 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 hemoglobin (HGB), platelet count (PLT), red blood cell count (RBC), white blood cell count (WBC), mean hemoglobin content (MCH) and mean corpusular hemoglobin concerntration (MCHC) were lower in gastric cancer patients than in controls, with HGB decreasing the most (β=-0.77, 95% CI: -0.82 ~ -0.71, P<0.001), and red blood cell volume distribution width (RDW) (β=0.13, 95% CI: 0.06 ~ 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 anaemia-related signs were more common in gastric cancer patients. The study found that WBC showed a gradual decreasing trend during the disease progression in GC patients.(P<0.001), and HGB, RBC and hematocrit(HCT) tended to increase with the duration of gastric cancer(P<0.001), but they were still lower than those of the control group. Conclusions This study indicates that GC patients are more likely to exhibit anemia-related abnormalities compared to healthy individuals. Additionally, certain blood routine parameters show significant changing tends with disease progression, providing valuable insights for clinical monitoring and management of GC.