Reasonable axial clearance setting of turbodrill stator and rotor can ensure free rotation of rotation system to avoid the damage caused by the stator and rotor collision. The axial clearance is very important for tool’s service life, but it is difficult to determine a optimal value, which only can be in a range because of the interference of parts machining errors, expression deformation and some other factors. In order to analyze the influence of axial clearance on the performance of φ89mm turbodrill, the theoretical analysis is carried out on efficiency and performance parameters calculation process in this paper combining with numerical simulation. Numerical simulation is made on single-stage φ89mm turbine with different axial clearance by using computational fluid dynamics(CFD) software. The results show that the axial clearance has only slight influence on φ89mm turbodrill in a reasonable range and can be negligible.