In view of the problems of thin coal seam thickness, soft coal seam, high gas content and high gas pressure in faer coal mine under the condition of complex stratum floor, through the analysis of coal seam occurrence state and geological conditions, combined with field drilling detection test, the branch hole layout design and construction scheme based on comb directional drilling technology are studied, The location of each branch point of comb directional drilling and the reasonable spacing of branch holes are determined to be 24 ~ 36m, and the directional drilling technology of floor comb directional drilling under complex formation conditions is formed. The field test application was carried out during the excavation of + 980m horizontal belt extension roadway in Fa'er coal mine. A total of 7 boreholes were constructed, with a total of 45 branches. The average gas drainage concentration of a single hole was 26.64%, and the average gas drainage purity of a single hole was 0.33m 3/ Min, the gas drainage effect has been significantly improved. Practice has proved that the application of this technology can effectively control the upper and lower exposed coal (coal seam groups) in the roadway excavation contour under complex geological conditions, and provide a certain theoretical support and technical reference for similar working faces.