To build an efficient grid-connected photovoltaic system with simple structure， one-cycle control， a non-linear control method， is applied to the inner loop current control. The conventional three-loop control performance is improved by keeping the switching frequency constant while maintaining an optimal current-tracking effect. Z-source converter boosts the photovoltaic panel voltage to meet the grid-connecting requirement， also achieve the maximum power point tracking. A system topology and one-cycle control model is proposed. Theoretical analysis and simulation results using Matlab/Simulink reveal that the output current of the inverter synchronizes with the grid voltage effectively. Small power experiments verify the proposed method.