The geometry of the impeller of a centrifugal blood pump has a significant effect on the hydraulic and hemolytic characteristics of the blood pump. In this study, a numerical simulation of the HeartWare ventricular assist device (HVAD) was performed based on the multiphase flow method to investigate the effects of flow channel width and top clearance on the hydraulic performance (head and efficiency) and hemolytic performance (normalized index of hemolysis) of the blood pump by analyzing the flow field and shear distribution of the blood pump. The results of the study show that the head of the blood pump increases with the increase of the impeller runner width, but the increase of the width leads to the expansion of the recirculation and stagnation area at the outlet of the impeller runner, which accelerates the formation of thrombus. The top clearance has less influence on the hydraulic performance of the blood pump, but increasing the top clearance helps to improve the hemolytic performance, and as the top clearance increases, the proportion of high shear force is significantly reduced, and the standard hemolytic index of the blood pump is also significantly reduced. In the comprehensive analysis, when the width of the impeller channel is 3.8 mm and the top clearance is 70 μm, the head and efficiency of the blood pump are 76.622 8 mmHg and 29.253 5% respectively, and the standard hemolytic index of the blood pump is 0.004 97 g/100 L. At this time, the blood pump has good blood compatibility as well as providing certain hydraulic performance. The results of this study can provide some reference for the structural improvement of HVAD.