Aiming at the problem that cement hydration heat release easily leads to hydrate decomposition when cementing deep water hydrate layer in the ocean. Heat storage agent (HSA) was prepared, and a cementing system that can be used in hydrate layer was proposed by using early-strength cement and heat storage agent. The research objective is to reduce the hydration temperature of cement on the basis of ensuring the early strength of the cement system so as to meet the cementing needs of the hydrate stratigraphic. In this study, a new heat storage agent was invented and its performance tested. The properties of different proportions of early-strength cement and Class G cement were compared. The performance changes of the cement system after adding heat storage agent were tested. The test results show that heat storage agent can resist the corrosion of seawater and alkali. After heat storage agent is added to the early-strength cement system, the hydration temperature of the cement can be greatly reduced, and the low-temperature (4 °C 24h) compressive strength can reach 5.1 MPa. The microscopic test shows that heat storage agents only affect the hydration rate and temperature of cement without affecting its stability. The results proved that the heat storage agent can be used as an environmentally friendly regulator of the heat of hydration for oil well cement. The results proved that the heat storage agent can be used as a regulator of the heat of hydration of oil well cement.