Abstract: In order to realize the gas extraction of the underlying coal seam under the influence of mining pressure relief in high gas mine, according to the complex engineering geological conditions in 5303 working face of Sihe Coal Mine, and based on the zoning of stress variation in floor rock due to mining, by comparing the trajectory simulation results of conventional vertical well and deviated well, combined with parameters of slant well drilling rig, this paper proposed the technology of using the slant drilling rig to construct the horizontal well for gas drainage while mining pressure relief. On this basis. The drilling trajectory design method of slant well was optimized, it effectively guided drilling construction, it also satisfied the requirements of geological targets. Natural flow exploitation after the completion shows that the use of slant drilling rig for CBM horizontal wells in complex engineering geological conditions is a feasible technology.