Aiming to realize the span-time heat storage of the greenhouse heat storage device and release the heat slowly, the design of thermal insulation materials outside the hot water storage tank and the structure of the water tank were optimized, the relationship between the combination of phase change materials inside the water tank and heat storage and release were studied. Experiments showed that the combination of thermal insulation coating+aerogel+rubberplastic thermal insulation cotton had a better thermal insulation effect. It reduced heat dissipation by 0.367MJ per unit time compared with a single thermal insulation material. And it was better to set the thickness of the water tank insulation material in the range of 80~120mm. The volume of the greenhouse heat storage device was 6~10m3 and the cylindrical water tank with a heighttodiameter ratio of 1∶1 had low cost and good heat storage effect. The composite phase change material combination increased the heat storage of water tank, the heat release process was optimized and the effect of slow heat release in stages was realized. A calculation model for the actual heat storage of the water tank was established with the size of the water tank and the phase change filling volume. Applying this model, the hot water storage tank was configured according to the heat load of different regions and the heat storage time of the water tank.