Abstract: The dynamic turn-off process of thyristor is complex and affected by multiple factors, which influence the precision of the commutation failure judgement directly. However, the thyristor model of fixed turn-off time used in the electromagnetic transient simulation cannot reflect the dynamic turn-off process of thyristor accurately. To model the turn-off process of thyristor accurately, we extracted the key influence factors such as current zero-crossing rate, forward current, and junction temperature by analyzing the dissipation characteristics of charge carriers during the turn-off process and investigated how the factors influence the turn-off characteristics. Based on the difference of dynamic dissipation and the characteristics of charge carriers during different periods of turn-off process, the nonlinear segmentation mathematical model of thyristor is established and the thyristor dynamic turn-off simulation model is established in PSCAD/EMTDC, and then the thyristor model is used to establish the converter model. Compared with the thyristor model of PLECS and the experimental test results of thyristor turn-off characteristics, the accuracy of the thyristor model is verified. Moreover, the accuracy of the converter model is verified by comparison with the experimental results of LCC physical dynamic simulation platform. The simulation results of the established model are compared with those of the traditional model under AC faults, and it is revealed that the established converter model can reflect the commutation dynamic process and commutation failure more accurately.