Considering the similarity in structures, using functions and control methods of the grid-connected inverter and active power filter, a unified control strategy is proposed. This strategy can realize both grid-connected power generation and active power filtering. Based on the analysis of the architecture and principle of the unified control system, harmonic and reactive current detection, voltage and current control method are designed for the system. Finally, the system can be controlled in the revolving coordinate reference frame. Using this unified control strategy, grid-connected generation, harmonics suppression and reactive power compensation are achieved at the same device, which exerts the advantage of distributed generation and improves grid power quality. At last, simulation results verify the validity and feasibility of the proposed strategy.