In order to effectively improve the max output power of photovoltaic power generation system, according to the output characteristics of PV and mathematical model, this paper proposes a new MPPT algorithm combining open circuit voltage and short circuit current, which uses open voltage, short circuit current and the S-function for MPPT. As the external environment constant changes will disturb frequently the PV system that introduces the algorithm, and the algorithm uses a lot of estimation algorithms in the process of theoretical derivation, thus threshold current and micro perturbation variable step length method are introduced in the algorithm. Current threshold reduces the disturbance of the system and energy losses. Micro perturbation variable step length method further corrects maximum power point of the system and solves the error problem brought by theory estimation. Experiments show that the open circuit voltage and short circuit current combined method after introducing the threshold current and micro step perturbation method can quickly and accurately track the maximum power point and improve the conversion efficiency.