Combined with UPFC equivalent model and power injection method or current injection method，the UPFC power flow model and the transient stability model are introduced by using PSASP custom function． The relationship between UPFC installation capacity and the change of tidal power in lines between Sichuan － Chongqing province is given． The dynamic characteristics of the lines between Sichuan and Chongqing，and the oscillation characteristics of transient energy are calculated． The results show that UPFC has a certain effect on improving the power distribution and suppressing the energy oscillation，but one unit capacity of UPFC can only change less than 0． 5 units power of the lines with UPFC，the leverage effect is pool，so the required UPFC capacity is larger．