Wanghe groundwater reservoir is a kind of coastal plain groundwater reservoir with underground dam and has double benefits of preventing seawater intrusion and providing fresh water. In order to correctly understand economic and ecological benefit,it is necessary to reasonably assessthe benefit value of Wanghe groundwater reservoir.The paper used related evaluation methods to analyze the benefit values such as saving of land requisition and evaporation, water conservation, adjustment and storage of flood,prevention of seawater intrusion, enhancement of groundwater level,restoration of wet land, water supply and increase of grain yield.The result shows that the values of benefit from big to small in turn land are saving of land requisition＞prevention of seawater intrusion＞water conservation,adjustment and storage of flood＞increase of grain yield＞water supply＞saving evaporation＞restoration of wet land＞enhancement of groundwater level, whose valuesare about 184, 66.2, 46.5, 26.47, 12.69, 9.04, 8.2 and 6.46 million yuan separately.Comparing direct benefit stemming from water supply, the Wanghe groundwater reservoir provided the greater and richer value of indirect benefit.This result can provide reference for benefit evaluation of similar groundwater reservoir.