As the main energy source of electric vehicle, lithium battery has an important influence on the safety performance of the whole vehicle, and the safety valve is the pressure relief device of the battery, when the internal pressure of the battery increases to a certain extent out of control, in order to prevent the explosion accident of the battery due to the increase of the pressure, the safety valve will automatically explode to release the pressure, and in order to reduce the experimental cost, in this paper, a finite element modeling method using strength index as the condition of safety valve opening is presented. According to the strength distribution, the open pressure of safety valve can be judged to meet the design requirements, and the weak position of strength can be found out, the notch depth of the relief valve groove is adjusted to help the structural designer predict the rationality of the model design at the initial stage of design.