As more and more flexible AC transmission devices are used in modern power systems,the research of optimal power flow (OPF) with thyristor controlled phase shifting transformer (TCPST) is facing new challenges. In order to ensure the security of the system,the equivalent power injection model of the TCPST access system is combined to establish the optimal power flow model with TCPST with the objective function of the minimum active power loss. In order to improve the convergence speed,the multicenter correction interior point method is improved. The iteration step of the affine direction is improved and the key mapping parameters is reconfigured. Based on the improved multicenter correction interior point method,the optimal power flow calculation test is completed in IEEE 14,IEEE 30 and IEEE 118 node networks,and the control ability of TCPST to line power flow distribution is tested. The test results show that the improved interior point method proposed in this paper is feasible and practical.