The lower group coal mining in the north China coal field is threatened by the Ordovician limestone aquifer and water-resisted layer mining with pressure is the strength, with a large amount of previous works, the top of the Ordovician weathering crust used as water-resisted layerwas was put forward, which is gradually accepted. But, factors restricting paleocrust water resisting performance remains unknown. Based on the problem,  the development thickness of paleocrust weathering, the filling degree of weathering fissure, the water bearing stratum and the development of geological structure have effects on the waterproof performance of paleocrust of weathering.