Objective To study the effects of different clearance conditions (equal upper and lower axial clearance, change of upper/lower axial clearance, axial displacement of blades) on efficiency and hemolysis performance of blood pump. Methods The blood pumps under three kinds of clearance conditions were numerically simulated by computational fluid dynamics. Results For efficiency, when the upper and lower axial clearance was equal, the lower axial clearance was unchanged and the upper axial clearance was reduced, the efficiency of blood pump could be improved by 0.85%, 1.71% and 2.90%, respectively. While the upper shaft clearance remained unchanged, the lower shaft clearance was decreased by 1.18%. For hemolysis, the increase of the clearance can reduce the hemolysis index (HI) under the first two clearance conditions, while the axial migration of the blade wheel would increase the HI. When the upper axial clearance was unchanged and the lower axial clearance was 0.3 mm, the HI was the largest, which was . When the upper and lower axial clearance was 0.7 mm, the HI was the smallest, which was . Conclusions Improving blood pump clearance is helpful to optimize the performance of blood pump. This study can provide some references for the design and optimization of interstitial structure of blood pump.