Abstract: Aiming at the problem of strata behavior Law of medium thick seam with shallow depth of thin bedrock, the article studies strata behavior law for 3-1 coal seam of Lijiahao Coal Mine with UDEC numerical simulation software and field test two methods. Studies show that the first weighting step distances is 20 m, periodic weighting step distances is 10 m. During periodic pressure period, the pressure is intense, short duration, the central pressure was large, early, long duration relative to both ends of the face; the abutment pressure in front of work face was not obvious, the smaller sphere of influence; face occurred stairs sinking, floor breaking movement spreaded to the top of the surface, the working face overburden only exists caving zone and fractured zone "two zone", there is no curve subsidence zone. Strata roof beam greatly decreased ability to transfer load in the direction of face advancing. The numerical results and field data are consistent.