A new approach to real time detection of harmonic and reactive currents for single-phase circuit was proposed. It makes use of some characteristics of triangle functions，and calculates the amplitudes of the fundamental active and the reactive current components in distorted current. Then it separates them from the ac components by low-pass filters. Finally，the fundamental active and the reactive current components were obtained. The circuit configuration of the proposed approach is simple，its dynamic response speed is fast，and its detection precision is high. It can detect any current component in distorted current or the sum of the harmonic and the reactive currents. The simulation and the experimental studies illustrate the performance of the proposed approach.