In order to improve the accuracy of the calculation of photovoltaic system short circuit current, this paper proposes that voltage drop degree, the output active of photovoltaic connected-grid inverter, and the positive sequence component of the grid voltage are the key factors, and the relationship between the three key factors and the peak value of the output current of PV connected-grid inverter is analyzed. The voltage power control strategy for the control objective of the output symmetrical three-phase sinusoidal AC current of photovoltaic connected-grid inverter is adopted. The output current model of the PV connected-grid inverter is established and the relevant parameters are identified based on system identification technology. Using the sum algorithm, the output short circuit current model of photovoltaic connected-grid system is obtained. The built model can be verified by MATLAB programming software. At the same time, compared with the constant power control simulation model built by PSCAD/EMTDC, the model can accurately reflect the output short circuit current of PV grid connected power generation system. This work is supported by National Natural Science Foundation of China (No. 51367017) and International S & T Cooperation Program of China (No. 2013DFG61520).