Supplementary exploration of hydrogeological conditions of lower series coal (upper part of No.16 strata and No.17 strata) have been carried out by No.3 Exploration Brigade of Shandong Coal Geology Bureau of Hegang coal mine in Jining city. It is regarded that major aquifers of Hegang coal mine are Quaternary sandstone aquifers, roof and floor sandstone aquifers of upper and lower part of No.3 coal strata in Shanxi formation, No.3 limestone, lower part of No.10 limestone, No.13 limestone and aquifer in Ordovician limestone of Taiyuan formation. Major water damages in lower series coal (upper part of No.16 strata and No.17 strata) are lower part of the limestone water and the Ordovician limestone water in Taiyuan formation. Hydrogeological conditions of ower series coal (upper part of No.16 strata and No.17 strata) belong to medium regional complex type. Its maximum water yield in mining is 816m3/h. Faults and fractures are the major factors in causing sudden water. Thus, effective countermeasures should be carried out to prevent water in the production period.