In order to study the damage evolution characteristics of cement mortar subjected to repeated high temperature and local water cooling, the central part of the cement mortar specimen was drilled. After heating the specimens to 400 ℃, water was poured into the hole for cooling, and then the operation was repeated continuously. Low field nuclear magnetic resonance technology, digital acoustic instrument and digital microscope were used to study the damage behavior of cement mortar specimens under repeated 400 ℃ and local water cooling. The results show that with the increase of high temperature treatment and local cooling times, the pore size and content of the small hole of the specimen increase continuously, while the pore size of the large hole decreases. After the first treatment, the performance degradation of the specimen is the most obvious, and the damage around the hole is greater than other parts due to local water injection cooling. Meanwhile, with the increase of high temperature treatment and local cooling times, the gray value corresponding to the peak probability density increases and moves to the right. In addition, the heat treatment weakens the cementing ability of cement mortar and sand particles. Repeated high temperature treatment further weakens the cementing ability of cement mortar and sand particles, and the wave velocity of specimen is reduced. However, the temperature stress generated by water injection cooling in the hole causes a sharp decline in the cementing ability. The effect of temperature stress caused by sudden drop of temperature on cementing ability of cement mortar and sand is much greater than that of repeated high treatment.