Abstract: In order to study the mechanism and prevention method of floor impact of gob-side roadway with large dip angle thick coal seam in deep mine, taking the engineering geological conditions of the working face in No.14 mining area in Huafeng Coal Mine as the background, through field investigation, theoretical analysis, industrial test, SOS microseismic monitoring and drilling cuttings monitoring, etc., the prevention and control of floor impact of gob-side roadway in 1412 upper roadway were carried out. The results show that the lower the horizontal stress and normal stress of surrounding rock, the less the energy stored in the hard rock stratum of floor, and the less the impact on roadway when impact damage occurs.The mechanism of floor impact prevention and control in gob-side roadway is revealed, and the risk of floor impact can be effectively eliminated by changing the energy accumulation and stress environment of floor.The optimum design scheme of reserving 5 m negative coal pillar along gob-side roadway to prevent floor impact is put forward, and the industrial test is carried out in 1412 upper roadway. The monitoring data of microseismic and drilling cuttings method show that the possibility of floor impact is effectively reduced.