Abstract: The location of an active power filter (APF) is extremely important to suppress harmonic current in coalmine underground power grid where the APF rate is limited. A new strategy for the best placement of an APF is developed in this paper. The strategy compute the harmonic similarity that relates the voltage at the nonlinear load bus to another bus in the power system first, and then determine the optimal bus to place the APF through selection algorithm. This strategy will both reduce the total harmonic distortion and simultaneously optimize the quality of power on an overall system. The validity of the developed strategy is verified by the simulation results