The present invention provides a system and method for clinical blood transfusion demand assessing and efficacy evaluating based on oxygen supply balance principle. The system includes a data collection module, a data storage module, a data processing module and a data display module. The method compares the difference between the actually detected increased hemoglobin concentration after transfusion and the expected theoretical increased hemoglobin concentration, and further accurately calculates the recommended infusion volumes of different blood receptors in the existing circumstances according to the accumulated data. At the same time, the system can automatically assess the therapeutic efficacy after each transfusion, and build up a new post-transfusion evaluation system based on the accumulation of the subjective feelings of the evaluation of the blood transfusion of the blood receptors. The method can realize the clinical evaluation of the erythrocyte transfusion demand and the scientific evaluation of the therapeutic efficacy of the erythrocyte transfusion, which reduces the pain of patients, reduces the workload of doctors, reduces the risk of blood transfusion and saves the blood resources. The method is an indispensable tool to guide the rational blood transfusion in clinical science.