The single-stage photovoltaic grid-connected system uses only once energy conversion to complete two functions: Maximum power point tracking (MPPT)and grid connected, so it has a large advantage of cost and efficiency. This paper research the Single Stage Three-phase Grid-connected Photovoltaic Inverter. Against the slow response of the DC bus voltage for the control of the traditional double-loop, being not conducive to the quick search of MPPT, this article makes the power feed forward algorithm be applied to the outer ring of the system control, and comparison with the traditional double-loop PI control. In addition, Against the unreasonable of the regulator design and the issues of the Parameters trial, PI regulator parameter design for in-depth research, Through detailed theoretical derivation, we come up with a new design PI regulator approach. The experiment verificates the new design method of PI parameters and the effectiveness of power feed forward control algorithm.