Aiming at the timevarying problem of surface crack safety attenuation of the pressure vessels, based on the simulation of the safety attenuation path for the surface crack, a description method for crack safety margin according to the PPV(product of the defect safety attenuation path and the velocity)was obtained. According to the law of the expansion rate of fatigue crack, the algorithm model of the remaining life for the pressure vessels with surface crack was obtained.The simulation test shows that the dynamic safety margin of the defect can be accurately and quantitatively characterized by the new method. The stress intensity factor can be obtained by the J integral in finite element method. Then remaining life can be obtained by Paris formula