Objective In centrifugal blood pump, the gap between impeller and volute is one of the key areas of the blood pump, which has significant influence on the hydraulic performance of the blood pump and blood damage. The effects of three different clearance conditions (equal upper and lower axial clearance, change of upper and lower axial clearance and axial displacement of blades) on blood pump efficiency and hemolysis performance were investigated. Methods The blood pumps with three kinds of gap conditions were numerically simulated by computational fluid dynamics. Results For efficiency, when the upper and lower axial clearance is equal, the lower axial clearance is unchanged and the upper axial clearance is reduced, the blood pump efficiency can be respectively improved by 0.85%, 1.71% and 2.90%. While the upper shaft clearance remains unchanged, the lower shaft clearance decreases by 1.18%. For hemolysis, the increase of the clearance can reduce the hemolysis index under the first two clearance conditions, while the axial migration of the blade wheel will increase the hemolysis index. When the upper axial clearance is unchanged and the lower axial clearance is 0.3mm, the hemolysis index is the largest, which is 8.65×10^(-4);When the upper and lower axial gap is 0.7mm, the hemolytic index is the smallest, which is 4.51×10^(-4).Conclusions Improving blood pump space is helpful to optimize blood pump performance. The results can provide some reference for the design and optimization of blood pump interstitial structure.