Abstract: In order to study the hydration development law of cement with different molding temperatures under continuous −5°C and 20°C curing environment, the hydration heat tests of cement paste with different molding temperatures of 5°C, 10°C, 15°C and 20°C were carried out under two curing systems. The hydration heat mechanism of cement paste with different curing systems and molding temperatures was analyzed. The effect of free water phase transformation on the performance of cement under negative temperature was explored. The hydration heat prediction model considering molding temperature ( 5~20°C ) under two curing systems was established. The results show that when the curing system is fixed, the hydration heat and hydration degree of cement paste increase gradually with the increase of curing age and mold temperature. The peak value of hydration heat difference and the equivalent age of hydration rate of 20°C curing and continuous −5°C curing are advanced by the molding temperature. Both negative temperature and low molding temperature will cause the age ' lag ' phenomenon in the hydration process. By analyzing the development law of hydration heat and its microscopic mechanism of action on cement paste, it is suggested that the molding temperature can be appropriately increased within a reasonable range to optimize the macro-micro performance of concrete under the negative temperature environment.