This research is aimed at the influence of the hydration environment on the performance of cemented paste backfill (CPB). In this experiment, the CPB was prepared by mixing water at three temperatures (5°C, 15°C, 30°C) and three pH (4, 7, 10). Testing the setting time of CPB and uniaxial compressive strength (UCS) of different ages, a scanning electron microscope (SEM) was used to explore the change rule of CPB performance under the joint action of pH-T. The results show that in terms of coagulation time, the coagulation time of the CPB under neutral or weak alkaline conditions decreases with the increase of temperature. The initial and final setting times of the CPB under neutral conditions are shortened by 20 min as the temperature rises. In alkaline conditions, the initial setting time of the paste at 15°C is 89 min shorter than that at 5°C, the initial setting time at 30°C is 84 min shorter than that at 5°C, and the final setting time is shortened by 95 min; under weak acid conditions, the coagulation time first shortens and then increases with the increase of temperature. In terms of UCS, under weak acid and low-temperature conditions, it is positively correlated with the curing age, but it gradually stabilizes. When the temperature is lower than 30°C, the paste strength first increases and then decreases with the increase of temperature and age, and the higher the temperature after 7 days, the faster the strength decreases. Under neutral conditions, it increases with the increase of temperature and age, 3–7 days; the higher the temperature, the faster the growth rate; the intensity of paste under weak alkaline conditions decreases with the increase of temperature and age. By adjusting the pH and temperature of the mixing water used in the CPB, the performance impact test of the CPB is carried out. It was found that the setting time of the CPB under weak acid conditions first shortened and then extended with the increase of temperature, and the low temperature is conducive to the development of its strength; neutral and weak alkaline conditions can effectively shorten the setting time of CPB, but weak alkaline conditions are not conducive to the strength development of CPB. This study provides a theoretical and experimental basis for the effect of mixed water on CPB performance under the coupled conditions of pH and temperature.