Abstract: Taking the welded work piece of TC11 alloy which is the conventional material of aero engine compressor as research object based on damage mechanics theory,the fatigue damage evolution law was studied.Fractal damage variables were defined with fractal geometry.The fatigue fractal damage evolution model was set up,which can be expressed through fractal damage variables.According to the results of fatigue experiments and the measuring results of fractal dimension on the surface of rupture work piece,the welded joint fatigue damage fractal evolution equation was also set up.Through further studying the relation between fatigue damage parameters and exterior load,a new way of forcasting fatigue life is given,which can connect the macroscopical fatigue damage life with the fractal dimension reflecting the microcosmic damage effect of structure.