This paper using the state space theory deduces the mathematical model for the single-machine infinite-bus systems with UPFC. And the eigenvalue method is employed to analyze the damping ability of UPFC. Based on the eigenvalue method analyzes conclusions, the oscillation frequency of the controlled power system is introduced to the conventional UPFC controller to change the fixed active power reference values. Then, based on the conventional UPFC controller, which adapting four independent PI controller, employs the principle of the PSS, this paper proposes a supplement controller for damping the low oscillation in the controlled power system. The detailed realization processing is stated in this paper. The simulations on the controlled power system without UPFC, with UPFC only and with UPFC integrated with the supplement controller by using PSCAD/EMTDC are made. The results reveal that the UPFC has the function of damping low frequency oscillation of the controlled power system itself, while the supplement controller may strengthen this effect dramatically.