The invention discloses a building water energy storage system based on photovoltaic power generation. Vacuum solar heat collection pipelines and a photovoltaic curtain wall power generation system are mounted on south outer wall of a building, a hot water reservoir is built in a basement of the building, a circulating water pump, a water supply pump, a water inlet pipeline, a water outlet pipeline and matched hydraulic engineering facilities are mounted in the hot water reservoir, and the hot water reservoir is provided with a matched automatic monitoring system. When irradiation conditions are good, water in the hot water reservoir is circularly pumped into the solar heat collection pipelines by the circulating water pump and heated by the solar heat collection pipelines, and the hot water reflows into the hot water reservoir and is stored. The hot water in the hot water reservoir is pumped into resident families by the aid of the water supply pump, and heat loads in the building are supplied. The photovoltaic curtain wall power generation system and a power grid jointly supply power for the circulating water pump and the water supply pump. According to the system, solar energy is collected, stored and distributed in a centralized manner, life demands are ensured, energy consumption is reduced, the use efficiency of energy is improved, user expenses are saved, heat insulation function is provided for the building by the aid of a photovoltaic curtain wall and the heat collection pipelines, and overall energy-saving effects of the building are enhanced.