Abstract: In order to break through the limitations of the existing abandoned metal casing detection technology for coalbed methane drainage in Sihe Coal Mine，realize the accurate detection of the metal cas⁃ ing position reduce the construction time and greatly improve the tunneling efficiency，according to the re⁃ quirements of field detection，two kinds of equipment，magnetic instrument and manhole cover detector， are selected to construct the detection model of coal body on the well，and a metal casing detection method combining far and near is innovatively proposed. By integrating a high-precision magnetic instrument and an electromagnetic induction manhole cover detector，a far-near field cooperative detection mode is con⁃ structed，which effectively overcomes the limitations of a single detection method. The research results show that this method can accurately locate the position of the metal casing of the abandoned coalbed meth⁃ ane drainage，and accurately determine the spatial position and distribution of the casing，so as to initially realize the safe excavation and mining within the effective detection range. Compared with the traditional method，the detection efficiency of this technology is increased by at least 50 times，the construction peri⁃ od is significantly shortened，the construction cost is greatly reduced，and the production efficiency and economic benefits of the enterprise are effectively improved.

Key words: coal mine, gas extraction pipeline, geomagnetic induction, magnetic instrument, man? hole cover detector