In the traditional single-phase grid-connected photovoltaic(PV) system, the output grid-current has the shortcomings of high harmonic distortion rate and slow dynamic response. In order to solve these problems, an improved method on the inverter is proposed. The inverter consists of full-bridge circuit and auxiliary circuit. With the multi-carrier PWM, the inverter produces output voltages in five levels, which can reduce the THD of the grid current. At the same time , this paper presents the power feed-forward algorithm based on traditional control method. The output power of PV array is added to the reference of current close-loop as power feed-forward, which improves the dynamic response to the input power changes. At last, the simulation results show the effectiveness of the proposed method.