The stress concentration effect of surface topography plays an important role in the fatigue properties of gears. The quantitative analysis method of the effect of surface topography on gear fatigue performance is the basic work of an in-depth study of the surface integrity of gears and the anti-fatigue manufacturing. Taking the spur gear with grinding as analysis object,and a method to estimate the fatigue life of tooth root bending fatigue with the surface topography is presented. The risk area of tooth root is obtained by finite element analysis.The risk area of the tooth root is measured by the white light interferometer, the statistical distribution parameters and the exponential autocorrelation function is obtained according to the surface topography,and using them to reconstruct the surface topography needed for the finite element calculation. Based on the finite element method,the stress concentration effect of tooth root surface topography is analyzed,and the fatigue life of tooth root is estimated based on the S-N curve of materials,and the quantitative relationship between the roughness R,a, and the bending fatigue life of the tooth root is given.