Severe voltage distortion due to power system harmonic resonance has been reported in recent years. The termination installation active filter was presented to resolve this problem. It operates as similar conductance for all harmonic frequencies whether in a fixed conductance command or in an automatic gain adjustment control. Therefore, its filtering capability is impeded by mismatching between the active filter and the radial line, and the voltage distortion may still be significant throughout the line. Distributed installation of active filters presented previously can address this issue effectively, but the practical application is limited due to their cost-ineffectiveness. This paper proposes a discrete frequency tuning active filter to suppress power system harmonics. The active filter operates as various conductance for individual harmonic frequency. Each harmonic conductance is dynamically adjusted according to the corresponding voltage distortion of the active filter installation point in response to increase or decrease of nonlinear loads, or variation of resonant frequency in the power system. The mismatching problem between the feeder and the active filter can be avoided effectively. Therefore, harmonic voltage distortion can be maintained at an allowable level throughout the feeder with lower peak current and lower rms current consumption, and various loads installed in the power system receive more uniform voltage waveform. Operation principles are explained in detail, and computer simulations and experimental results validate the effectiveness of the proposed approach.