Abstract: In order to realize safe and high efficient mining under highway,the ground subsidence law and mining technology under highway in loess hilly-gully region were studied deeply through the comprehensive application of the engineering practice,field observation,numerical simulation and theoretical studies.The results showed that：because of the coal seam buried shallowly,the heavy thickness and the low strength of the Quaternary alluvium,the overlying rock strata in stope damaged severely and water conducted zone reaching to surface directly.At the initial of the fully-mechanized top-coal caving，step cracks appear inside of gate roads and outside of the cutting hole.Fracture trend parallel to the stope boundary,with small step throw.When coal mining reach or exceed the full mining,rock mass is cut down as a whole along the coal wall at the mining boundary,and big step cracks appear at the surface.The surface cracks are greatly affected by terrain.The surface cracks are well developed under the action of gravity and coal mining subsidence.The thick soil lager under subgrade can absorb part of the mining subsidence deformation,and this played a certain role in reducing highway damage.The coal pillar for highway safety can be designed by the steps cracks angle,and these pillars are not mined.The highway can run safely with some measures taken.This research provides a reliable reference for coal mining under highway with similar geological conditions.

Key words: Loess hilly-gully region, Fully mechanized top-coal caving, Mining under highway, Steps cracks