A pneumatic grinding device was designed which could be used to repair small gaps and damage of engine blades.In order to further study the grinding head’〖KG-*3〗s speed characteristics under the effect of air pressure, to clarify the basic law of the grinding head’〖KG-*3〗s rotation speed with time under different air pressures,fluid mechanics theory and dynamic grid technology were applied to make numerical simulation of grinding head’〖KG-*3〗s passive rotation.Based on numerical simulation results,the Sigmiod deformation function,numerical integration and interpolation were used to get the mathematical model among air pressure,time and rotation speed. The results show that the simulation can effectively simulate the actual state of the flow field, the data are in agreement with the test results, the calculated error of grinding speed and experimental value is less than 10%, the validity and feasibility of the numerical simulation method are verified.