Abstract ：According to NC grinding principle and the tooth mathematical models of bevel gear，the forming principle and influencing factors of generating surface roughness of bevel gear are analyzed by the single blade method which used for the cup-shaped grinding wheel. Based on the analysis method of machining motion trajectory，the nodes and contact line vectors of NC grinding tooth are computed. Calculations of 3D theoretical residual area height are translated from ones of 2D along tooth highness cross section by grid compartmentalization，and the computing model of grinding surface roughness are setting up by taking a plastic scratch distortion into account. The computing and test validation analyzing results of grinding tooth surface roughness Ra of spiral bevel pinion have many. Firstly，the Ra values are raised a little as increasing the generation speed，while they are distinctly decreased as increasing the wheel speed. Secondly，when grinding depth(a) is more than 0.1 mm，they are increased greatly as heightening a，and also affected differently by other factors. Finally，the maximal absolute value of relative error between testing Ra values and computing ones is 17.1 percent，this display that the theoretical model of grinding tooth surface roughness has better precision. These provide a foundation for the control of grinding tooth quality of bevel gear.