Flywheel type flexible power conditioner（FPC） is a power system stability control device based on the energy storage theory.To demonstrate the effects of FPC on the power system damping characteristics， the eigenvalues of a double-machine infinite-bus system with a FPC are investigated. The impacts of two FPC parameters on the power system damping characteristics are also studied， i.e. the FPC response speed for power adjusting and the FPC adjustable power. Simulation results indicate that the FPC effectively increases the total damping resources of a power system and optimize the damping allocation. Especially， the FPC dynamic active power control capability significantly improves the damping characteristics， e.g. mitigating low frequency oscillations in a power system.