Abstract: The multi-layer goaf has complex structure.It is difficult to grasp the distribution of holes，fissures，residual coal pillars and roadways.To ensure safety，reasonable engineering investigation must be chosen before planning and utilizing the land on the goaf.Lots of theoretical researches and engineering practice proved that during the construction process of exploration holes，the characteristics of fracture development and the height of water flowing fracture zone were preliminarily determined through observing drilling fluid leakage，drills failure and abnormal footage.And the accuracy and effect of detection was greatly improved by borehole television with high resolution after the construction completion of observing holes.Combining with the observation method of drilling fluid leakage and borehole TV system to make the detection analysis on multi-layer goaf，the developing depth of caving zone and fracture zone were determined.Based on grasping the geological and mining conditions and the observation information，the stability of the overall structure of the relevant regional gob can be judged，thus providing some experience and reference for the study of related issues.

Key words: Multi-layer goaf, Loses observation of flush fluid, Borehole TV system, Comprehensive analysis