The influence of temperature on the compensation effect of MgO expansive agent in cementbased materials is crucial. This article reveals the temperature sensitivity of MgO expansive agent in cementbased materials by testing the restricted expansion rate, mineral composition, morphology and distribution of hydration products, and hydration degree of MgO expansive agent of cement mortar under different curing conditions. The results show that with the increase of curing temperature, the restricted expansion rate of medium speed MgO cement mortar containing 8% (mass fraction) significantly increases, especially under the curing condition of 50 ℃, and 28 d restricted expansion rate is 1.7 times that of 25 ℃. There are differences in the impact of different curing conditions on the expansion of MgO. In the hightemperature rise slow cooling variable temperature curing condition, the cement mortar containing rapid MgO has the highest restricted expansion rate, and the expansion rate decreases significantly during the cooling process. However, in the lowtemperature rise fast cooling variable temperature curing condition, the hydration of the system continues, and the MgO expansive effect can be sustained. In addition, the reaction degree of MgO in cement paste also increases with the increase of curing temperature, which is 25%~65%. The hydration product Mg(OH)2 mainly exists in the gel state, but with the temperature rising to 50 ℃, some gel like Mg(OH)2 is transformed into lamellar crystals, further optimizing the microstructure and expansion performance of cementbased materials. This study provides a reference for understanding and optimizing the application of MgO expansive agent in cementbased materials.