Abstract: In order to achieve safety mining under the loose aquifer, based on the hydrogeology condition and engineering geological condition of bottom aquifer of unconsolidated formation (fourthly aquifer) in No.13 mining area of Qingdong Mine, it discusses the distribution characteristics of thickness, water quality condition, coefficient of permeability (K), and water storage coefficient (u^*) of Qingdong Mine No. 13 mining area and researches the water abundance condition of the fourth aquifer. The results show that Qingdong Mine No.13 mining area is a weak water abundance aquifer and the required safety coal pillar type should be sand proof safety pillar according to Buildings, Water, Railway and Main Roadway of Coal Pillars and Mining Regulations.