Evaporation of ground water is a part of moisture circulation in the field. And it is a main natural form in which water transmits from the ground water to the soil water and atmosphere water. According to the simulated experiments, we study the relationship among the evaporation, depth of groundwater table and negative pressure. By theoretical analysis of the experimental results, the main conclusions are drawn as follows. There are two abrupt points in every Q H curve. The locations of the abrupt points are separately in step with the height of top of the capillary fringe and the height of maximal capillary rise in the soil section. When the depth of ground water table H is small, the evaporation flux of ground water is large. While the depth of water table exceeds the maximal capillary rise of media in vadose zone, the capillary rise breaks up and evaporation flux of groundwater is small. The water content ratio in ground surface tends to be zero and the surface of soil tends to be drought. These conclusions show that the maximal capillary rise of media in vadose zone is an important value in regulating rational depth of ground water to reduce the evaporation of ground water and to increase effective quantity of water resources. In the meantime, these conclusions are of important theoretical and practical significance to reduce the evaporation of ground water, to prevent and cure the salinization of soil, and to make full use of and protect water resources in the northern plains in China. Evaporation of ground water is a part of moisture circulation in the field. And it is a main natural form in which water transmits from the ground water to the soil water and atmosphere water. By theoretical analysis of the experimental results, the main conclusions are drawn as follows. There are two abrupt points in every QH curve. The locations of the abrupt points are compared in step with the height of the top of the capillary fringe and the height of maximal capillary rise in the soil section. When the depth of ground water table  H is small, the evaporation of of ground water is large. While the depth of water table exceeds the maximal capillary rise of media in vadose zone, the capillary rise breaks up and evaporation flux of groundwater is small. The water content ratio in ground surface tends to be zero and the surface of soil These conclusions show that the maximal capillary rise of media in vadose zone is an important value in regulating rational depth of ground water to reduce the evaporation of ground water and to increase effective quantity of water resources. In the meantime, these due are of important theoretical and practical significance to reduce the evaporation of ground water, to prevent and cure the salinization of soil, and to make full use of and protect water resources in the northern plains in China.