Abstract: Based on current-injected method and power-injected method, two different models of two-core symmetrical thyristor controlled phase shifting transformer (TCPST) are proposed in this paper. Using the user defined model interface of power system analysis software package (PSASP) 6.2, two corresponding models appropriate to PSASP are established, which can be used to analyze the power flow. In order to prove the validity of the two models , a 3-machine 9-bus system for calculation example is established. Calculation result validates the two models are effective to modeling a TCPST.