Abstract: UPFC (unified power flow controller) can control bus voltage, line flow and enhance system dynamic stability using different controlling strategies. Its supplementary damping controller may exert great importance to system dynamic stability. Firstly, this paper adds UPFC into the system linearized model and applies DTA (damping torque analysis) to UPFC analysis and deduces the DTA sensitivity. On this basis, the DTA model considering time-delay is obtained according to the frequency domain model of time-delay, which can be applied to UPFC supplementary controller parameter tuning combined with the phase compensation method. Finally, validity and feasibility of the proposed model are demonstrated in two practical cases. Simulation results indicate the method could inhibit oscillations effectively and improve system stability.