The invention discloses a heat storage structure achieving flow heat exchange in phase-change materials through capillary tubes. The heat storage structure comprises a shell (1) which is of a cuboid box type structure as a whole. A circle of heat preservation layer (2) is arranged on the inner side of the shell (1). A water inlet plenum chamber (3) and a water outlet plenum chamber (4) are arranged at the opposite corners in the shell (1). The water outlet end of the water inlet plenum chamber (3) is provided with a plurality of the first main capillary tubes (6) which are distributed at equal intervals in a sealed mode. The water inlet end of the water outlet plenum chamber (4) is provided with a plurality of the second main capillary tubes (9) corresponding to the first main capillary tubes (6) in a sealed mode. The heat storage structure is simple in structure and ideal in heat dissipation effect. By the adoption of the heat storage system, a sewage source heat pump can be used for making hot water in an off-peak electricity consumption period of time at night, one part of the hot water is used for heating, and the other part of the hot water is used for heat storage. The heat is released in the daytime. Not only can renewable energy be used but also operation cost is reduced.