Thyristor controlled phase shifting transformer (TCPST) has fast response characteristic, and can improve system stability. In order to realize the transient stability calculation of large-scale power system with flexible AC transmission system (FACTS) equipment, an electromechanical transient simulation model of TCPST is proposed in this paper. Considering the electrical part and control structure of TCPST, the mathematical expression of TCPST node power injection model is deduced through model equivalence and equivalence transformation. And the gear control model is implemented with supplementary damping controller. Furthermore, in view of the numerical oscillation problem caused by the discrete switching characteristics of gear in the TCPST simulation model, a suppression scheme using the filter to process the injected power is proposed. Finally, the electromechanical transient model is built by using the AC/DC power system calculation and analysis software, and the model is applied to the case of China Southern Power Grid. Through the comparison of the simulation results of the example system by DSP, BPA and PSCAD respectively, the correctness of the proposed transient model is validated, and the electromechanical transient modeling method provides reference for the simulation and modeling of other FACTS equipment.