The deterioration of murals, sculptures, and cliff bodies in cave temples caused by moisture migration remains a significant challenge in the field of grotto conservation. Taking the Yulin Grottoes, situated in an arid environment, as an example, this study examines the occurrence of moisture on the dome of Cave 6 during rainfall, despite the implementation of measures to prevent direct infiltration of precipitation. Samples from the grotto excavation stratum were collected to conduct moisture migration simulation experiments under the influence of rainfall, temperature, and air pressure. The relationship between environmental factors and the moisture content of the grotto surrounding rock was analyzed in conjunction with field monitoring data to identify the primary factors influencing moisture migration in conglomerate grottoes in arid environments. The findings suggest that air pressure, precipitation, and temperature are the predominant factors influencing moisture migration within the surrounding rock formations of the Yulin Grottoes. The migration rate of moisture in conglomerate samples exhibited a positive correlation with the gradient of external environmental conditions and a negative correlation with the distance from the loading position. Additionally, pore air pressure has been demonstrated to play a significant role in driving moisture migration in the surrounding rock of conglomerate grottoes during rainfall events. The findings provide a scientific basis for managing water-related hazards at the Yulin Grottoes and offer references for the conservation of similar cave temples.