The safety hot water stock of solar central water heater plays an important role in balancing the user demand and energy consumption. To design and establish a suitable safety hot water stock model can effectively reduce the energy consumption in the auxiliary heat source in the system. The credibility theory recently has been widely applied to solve the problems in engineering uncertainty, product management, inventory management and the ambiguous design in power system, etc. All heat losses parameters of solar central water heater are analyzed in this paper with the purpose of designing a safety hot water stock model suitable for solar central hot water engineering based on the credibility theory and further the optimized result to control the solar central water heater being used in the field control system of the solar system to help the solar central water heater to reduce auxiliary heat source energy consumption. The running results show that the model of the optimal solution design in this paper can improve energy utilization and reduce energy consumption in the auxiliary heat source.