Abstract: Grinding surface roughness is an important evaluation index to characterize grinding quality, and grinding micro-surface topography is an important factor to determine surface roughness. It is difficult to predict the grinding micro-surface topography and roughness of workpiece in advance based on experience. To solve this problem, a method based on numerical modeling and experiment was proposed to predict grinding surface roughness. Taking the needle valve body in the precision coupling of the injector nozzle as the research object, a numerical model of the grinding wheel was established based on the fact that the height of the grinding grains obey the normal distribution. On this basis, the grinding microscopic surface topography was generated by establishing the motion trajectory equation of grinding grains on the surface of the grinding wheel, and the surface roughness was accurately calculated. Finally, the effectiveness of the method proposed in this paper was verified by grinding experiments. The method proposed in this paper can provide method support for efficient, high quality and low cost processing of needle valve body.