The paper analyzed the difference and the error of trans-mechanism of moisture between the lysime-ter and th e natural unconfined groundwater system.The result shows that the water table dynamic,the moisture storage,the moisture transport and so on exist some different in the lysimeter and in the natural condition.That caused the error compared with scene of natural condition in groundwater evaporation and its precipitation infil-tration recharge as well as the error varies on the groundwater table.The less deep-water table under ground,the greater error follows.Especially,measured data of water table within1.5meters under ground should make a technical treatment.Otherwise,it would lead an even greater error.