Phase change materials have good properties such as high thermal capacity and constant phase change temperature. Their potential use in solar energy storage is promising. Tests of exposure and constant flow rate are performed to investigate the thermal performance of a domestic solar water heater with solar collector coupled phase-change energy storage. Due to the low thermal conductivity and high viscosity of Phase change materials, heat transfer in the Phase change materials module is repressed. The thermal performance of the domestic solar water heater with solar collector coupled phase-change energy storage under exposure is inferior to that of traditional water-in-glass evacuated tube solar water heaters with an identical collector area. domestic solar water heater with solar collector coupled phase-change energy storage also performs more efficiently with a constant flow rate than under the condition of exposure. Radiation and initial water temperature have impacts on system performance; with the increase of proportion of diffuse to global radiation and/or initial water temperature, system performance deteriorates and vice versa.