Automobile rear axle is the core load-bearing part of automobile chassis,its main damage form is fatigue failure under alternating load. It is of great significance to quantitatively evaluate the fatigue sensitivity of rear axle to realize the lightweight design of automobile and to improve the effective service life and safety of automobile. Firstly,the three-dimensional finite element model of automobile rear axle was established, and the maximum vertical force was selected for strength calculation,and the stress and strain state of automobile rear axle was obtained. On this basis,the fatigue life and damage distribution of the rear bridge are calculated based on n Code Design-Life,and the sensitivity of various parameters to the fatigue life is analyzed by response surface method. The results show that the fatigue failure of the rear axle first appears at the half axle sleeve pipe,elastic modulus has the most obvious effect on fatigue,the thickness of leaf spring seat is next,and the influence of bridge shell thickness,poisson’s ratio and bridge envelope thickness decreased successively.