Abstract: Acid mine drainage gushing from unknown source after coal mine closure is the key problem that puzzles the ecological restoration of mining areas. Due to the southern coal mining areas in China generally exist “complex terrain conditions, large mining base, multiple points and wide areas” and other problems, it is difficult to identify large-scale underground pollution sources. In order to investigate and study the water-rich space of coal mines in areas with complex terrain and trace the source of acid mine drainage gushing on the surface, the historical abandoned mine in Yanshi Town, Longyan City, Fujian Province, which is located in the depression zone of southwest Fujian Province was taken as an example. Use the semi-airborne transient electromagnetic method with Unmanned Aerial Vehicle, the low resistivity characteristics surrounded by high resistivity for detecting target and according to the resistivity difference between water-rich area and surrounding rock to detect the abnormal water content area within 300 m below the surface with multi-source data, analyze the water content of the abnormal area, and define the geographical location of the water-rich space, provide a scientific basis for the treatment of acid mine drainage in abandoned coal mines. The results show that: ① The semi-airborne transient electromagnetic detection technology has a high sensitivity to the detection of underground water-rich space, and the low-resistivity anomaly area covered by high resistance can effectively reflect the water content of underground space; ② Historical gob areas are widely distributed in the study area, but not all the historical gob areas are water-rich. Using semi-airborne transient electromagnetic detection technology and geological profiles, a total of 8 water-rich areas, a large number of nearly circular water-rich channels and 3 water-rich areas in fault zones are identified; ③ The historical goaf in the study area is not the main underground water-rich space. Compared with the water content of the goaf, the water content of the near-circular tunnel and the waterlogging zone of the fracture zone is also particularly important for the treatment of water gusher in the surface acidic mine.