Abstract: Aiming at the characteristics of shallow buried coal seam and poor geological conditions of water retaining mining in the ecologically fragile area of Western China, the concept of passive water retaining mining, which used to block the leakage of groundwater as the main technical means, was broken through, and the concept of underground water protection of coal mine underground reservoir with “diversion, storage and use” as the core was put forward. Through the research in recent years, the basic theory and engineering practice of coal mine underground reservoir have made great progress A lot of achievements have been made.This paper systematically summarizes the six key technologies of coal mine underground reservoir, including water source prediction, storage capacity design, reservoir site selection, dam structure, safe operation and water quality guarantee. The first three technologies are the premise of underground reservoir construction in coal mine. The research mainly involves the engineering geology and hydrogeological conditions of coal mine, the movement law of underground water during coal mining, and the evolution of space and bulking property of caving rock mass in goaf. The research of dam structure mainly involves the stability of coal pillar dam and artificial dam under various complex forces and the connection between them. The main research of safety and water quality guarantee is to establish the safety monitoring system of underground reservoir and the mechanism of mine water purification by the caving rock in goaf. The utilization of underground and ground water resources of underground reservoir in coal mine is expounded, which realizes the transformation of mining area from large water consumption to water supply source. On the basis of summarizing the relevant research results, with the aim of coal-water-ecological coordination, the direction of coal mine groundwater reservoir research is forecasted.