To expand the application radius of hemihydrate phosphogypsum (HPG) as filling cementitious material, a new breakthrough of HPG resource utilization technology was realized. A model HPG the change of heat release in hydration reaction during storage is sought to understand the change of gelation properties. The free water content and temperature monitoring tests of HPG reactors with initial temperature of 35, 40, 60 and 80℃ were carried out first. It was found that the law of HPG free water content change was in accordance with the first-order reaction kinetic model. After that, based on the basic theory of thermodynamics and chemical reaction kinetics, a HPG hydrodynamic model of the relationship between storage temperature and time was proposed. Lastly, COMSOL Multiphysics numerical simulation software is used to embed the thermal dynamic equation of HPG hydration reaction into the heat transfer and ODE module to simulate the temperature of the HPG reactor. The simulation curve of the temperature change of the reactor is in good agreement with the test results. The reliability of the proposed model is verified.