Abstract: Based on a high watery of the loose apuifer in the overburden stata above the mining seam of No.21 seam in Zhacgu No.1Mine in orderto define theweathering zone scope and the water res stance and isolation features of the base rock and to reaize a saety coal mining under the water bodyapoint oading strength test.dry saturated water absorption rate test and disintegration test of the ock samples wereconducted.The study on the variation law of each tet idex with the depth varied was appied to defie the limio f the baserock veathering zone and the wateresistance and iso ation featues afer the weathering role conducted. The testresults showed that a distance of 21.5 m to the bottom linit of the loose stratum was te limit of the base rock weatheing zone. wihin the ~ 10 m scape,the weatherng zone of the base rock was the mud type rock nainlythe dry saurated water absoption rate was over15% and the disintegration was rapid.The weatering zone with excellent water res istance and isolation features could be favorable to the crack closed and to restrain the development of the waer fov crack zone. The dry saurated water absorption rate of the sandstone was ov and the water resistance and isolation waspoor.With a igh endurin disintegratonthe sandestone would not be favorable to the water flow crack closed.