Abstract: At present, there are more and more power electronic devices in the power system, and the power electronic trend of the power system is increasing. Aiming at the time-varying admittance matrix of binary resistance model of power electronic switch and the low accuracy and high power loss of traditional L/C model in transient process, a constant admittance model of power electronic switch based on exponential integration is proposed in this paper. This model combines the characteristics of binary resistance model and traditional L/C constant admittance model, takes into account the power loss and transient process in the actual working process of the switch, and ensures that the admittance matrix remains unchanged, so as to improve the simulation efficiency. In other words, resistance R_on and R_off are introduced into the on and off equivalent branches of the traditional L/C constant admittance model to form a first-order dynamic circuit with damping effect. It is proved by the terminal value theorem that the proposed model is consistent with the binary resistance model in steady state. Then, the L/C parameters of the proposed model are determined by spectral radius analysis, so that the convergence process of the proposed model is shorter and the power loss is lower than that of the traditional L/C model. Finally, the effectiveness and feasibility of the model are verified by an example.