Abstract: Groundwater is an important carrier of hydrocarbon migration in sedimentary basins.Hydrogeological characteristics can control or influence reservoir boundary.On the basis of classifying water-bearing rock series,combining hydrodynamic field with hydrochemical field,the hydrogeological conditions of main water-bearing rock series have been studied in the Wuerxun Sag of the Hailaer Basin.It is divided into 3 different types of hydrogeological zones: a)actively alternating—oxidation zone,which is highly open and is unfavorable for oil and gas accumulation;b)slowly alternating—weak reduction zone,which is more favorable for reservoir formation;c)alternation blocked—reduction zone,which is closed in high degree and is conducive for reservoir formation,hence is the most favorable target area for exploration.