According to the research and application status of variable power output control in two-stage grid-connected photovoltaic (PV) system, a novel variable power output control strategy based on reference current mode is proposed. By comparing the constant power with the PV power and changing the current of PV, this method is able to realize two PV power output modes, i.e. MPPT mode and constant power generation (CPG) tracing mode, and also can control the PV power output fast and effectively under different solar irradiation. A small signal model of Boost converter is built by using the proposed control strategy. It analyzes the impact of PV array equivalent impedance on pre-stage system stability under different power in detail and introduces the controller design of two modes power output. Finally, the simulation and experiment results verify the effectiveness of the proposed control strategy. This work is supported by National Natural Science Foundation of China (No. U1804143 and No. 61703144) and Key Science and Technology Project of Colleges and Universities of Henan Education Department (No. 17A470010).