Abstract: Based on the three parameters reliability analysis model and the fatigue theory of gears,a new reliability analytical method for the bending fatigue strength of tooth root is proposed by use of blending stochastic finite element method.This method takes into account such random factors for the reliability of gears,as load,fatigue limit,the material parameters and radius chamfer of tool.Analyses completed with this method indicate:The radius chamfer of tool has unignorable effect on the reliability of gears' bending fatigue strength;In the linear elastic problems,the Young's modulus has no effect on the structure reliability;The Poisson ratio has a little leverage on the gears' reliability;But the gears' reliability reduces with the increase of variation coefficients of the above mentioned random factors;So the gear's reliablity will increase as the skewnesses of fatigue limit and the radius chamfer of tool rise.But the skewness of load has an inverse influence.This paper also considers the modified coefficient's (no random factor) effect on the gears' reliability.