In order to study the damage evolution characteristics and crack propagation of high temperature cement mortar after local water cooling, a hole was drilled in the middle of cement mortar specimen. The specimen was heated to 200 ℃ and 400 ℃, and then water was injected into the hole for local cooling. The damage behavior of cement mortar specimen under high temperature and local water cooling was studied by low field nuclear magnetic resonance (NMR). The results show that with the increase of the heat treatment temperature, the pore size and content of the small hole of the specimen after local water cooling increase continuously, while the change of the large pore is not particularly obvious, and the damage degree of the specimen increases correspondingly. At the same time, after high temperature and local water cooling treatment, the peak of the probability density distribution of the gray value of magnetic resonance imaging specimens moves to the right with the increase of temperature. And the higher the temperature is, the greater the increase of the gray value corresponding to the probability density distribution function is, which is consistent with the change of T2 spectrum. Finally, the distribution of temperature and temperature stress of cement mortar specimens after high temperature and local water cooling were solved, and the crack germination and propagation range of locally cooled cement mortar specimens after 200 ℃ and 400 ℃ were solved based on the maximum tensile stress criterion.When the temperature is 200 ℃, the temperature stress produced by local water cooling is not enough to cause crack initiation.