Two typical residential solar hot water engineering cases located in Chifeng and Tianjin are tested respectively. The relationship between the outdoor air temperature, heat of solar collector system, system cycle heat supply and the time has been studied. The energy of each part of the solar hot water system is calculated from the angle of energy balance. It finds that solar fraction as an important reference index of the system design has certain limitations when evaluating the actual running system. In order to conduct a more comprehensive assessment of the actual energy efficiency of solar hot water systems, three new evaluation indicators are defined for solar energy utilization ratio, conventional energy efficient replacement rate, system heat dissipation ratio.