Objective To investigate the effects of rounding on the prediction of flow field and hemolysis for FDA benchmark blood pumps by using the method of computational fluid dynamics（CFD）. Methods Key properties such as hydraulic characteristics, mean velocity distributions and hemolysis index of FDA benchmark blood pump under three operating conditions were simulated, and the influence of the above simulation result was further compared when the impeller was equipped with or without rounding. Results The rounding of blood pump impeller had impacts on pump head (the maximum percentage difference between the impeller with rounding and without rounding was 57.38%), velocity distributions, which led to a considerable impact on predicted hemolysis levels (the maximum error between the impeller with rounding and without rounding was more than one order of magnitude). Conclusions Impeller with rounding was beneficial for optimization of blood pump performance. The research findings are of great importance for better use of CFD to aid the hemocompatibility design of blood pump.