According to the photovoltaic system output voltage curve in the change rule of the maximum power point on both sides of the different slope, the left slope of MPP changing smoothly, right relatively steeply, on the basis of maximum power point tracking control method research, and combined with the existing variable step-size incremental conductance method, this paper presents a optimization algorithm of the piecewise variable step-size incremental conductance method that a exponential function is used to adjust the tracking voltage step on the left side of the MPP, and a logarithmic function is used to adjust the tracking voltage step on the right side of the MPP. Simulation results show that this method is good for photovoltaic system maximum power point tracking, effectively reducing the power loss near the MPP caused by the oscillation of step-size in the tracking process, and improve the power output efficiency of PV system.