Abstract: The state variables change of Photovoltaic alone with its control variables is studied on the basis of photovoltaic generation system research. A model of photovoltaic external characteristic model is established as well. The model included its active power output as well as reactive power output. The power of each photovoltaic can be variable in a wide range based on the local temperature, illumination intensity and weather conditions when these DGs are connected to the grid. As a result, the power flow of distribution network may be changed and it will also lead to a higher network losses and fluctuated voltages. A novel model for analyzing active power change of photovoltaic is established, besides, the feasibility and influencing factors of reactive power of photovoltaic is demonstrated. In the end, the corresponding method of dynamic power prediction of photovoltaic is proposed to get the optimal active power output and reactive power output. The results of an example show that the efficiency of photovoltaic and the stability of power system can be largely improved by using the method.