Abstract: Objective To analyze the changes in blood composition before and after collection of chimeric antigen receptor T-cell (CAR-T) precursor cells from patients, in order to provide reference for CAR-T precursor cell collection. Methods A total of 129 patients, who underwent CAR-T precursor cell collection by COM.TEC-type blood cell separator in Department of Hematology in the Affiliated Hospital of Xuzhou Medical University from January 2022 to December 2023 were selected as research subjects for retrospective analysis. The white blood cell (WBC) count, lymphocyte count, red blood cell (RBC) count, hemoglobin (Hb), hematocrit (HCT), and platelet (PLT) count before and after collection, and the changes in electrolytes, such as Ca²⁺, K⁺, Na⁺, and Cl^-, were observed, while adverse reactions during collection were recorded, and the reasons for changes in blood composition were analyzed. Then, gender, age, body weight, disease types and pre-collection WBC count, lymphocyte count, PLT count, HCT and end-product mononulear cell (MNC) count were analyzed by multiple linear regression. Results CAR-T precursor cells were successfully collected in all 129 patients, and the mean MNC count was 7.4×10⁹/L (1.4×10⁹/L-38.0×10⁹/L), without severe single-collection adverse events. Lymphocyte count, RBC count, Hb, HCT and PLT count significantly decreased after collection, compared with those before collection (P<0.05), while WBC count increased withont statistical differences (P>0.05). Furthermore, K⁺ and Cl^- concentrations significantly decreased (P<0.05), and the differences in Ca²⁺ and Na⁺ concentrations were not statistically significant (P>0.05). Multivariate linear regression analysis showed that pre-collection WBC count, lymphocyte count, HCT, and body weight were closely associated with MNC count (P<0.05). Conclusions Collection of CAR-T precursor cells in patients by COM.TEC-type blood cell separator is safe and feasible. Maintaining high WBC count, lymphocyte count, HCT and appropriate body weight before collection can effectively improve collection effect.