In a solar photovoltaic power system, an increase in temperature of the template gives rise to a decline in power efficiency. So it is necessary for the photovoltaic template to be effectively cooled so as to reduce its influence on the power generation system. On the basis of water-cooled photovoltaic template experimental system, the variation laws of template temperature has been studied with some changing factor such as amount of cooling water, radiated power and so on. With the adoption of Sieder-Tate formula, the heat exchanger mathematical module has been established and the variation of template temperature with the amount of cooling water has been calculated and analyzed under the different power and the inlet water temperature. It turned out to be that the theoretical calculations and experimental data are consistent with each other. The errors meet engineering requirements. It also can give a reference to the design and application of water-cooled system.