The ecological water requirement of Robinia perseudoacacia can be expressed by the evapotranspiration of trees in growing season.It can be influenced by weather,vegetation,and soil moisture.If soil moisture is above temporary-wilt or growth-retard,tree growth can be sustained,basically or normally.Therefore,soil water contents for temporary-wilt and growth-retard can be taken as the minimum ecological water requirement and the suitable ecological water requirement of Robinia perseudoacacia,respectively.They can be estimated by introducing soil factor and tree species factor to potential evapotranspiration with Penman formula.Accordingly,the ecological water requirement(May to Oct.) for Robinia perseudoacacia in Yangou watershed is estimated.The minimum and suitable ecological water requirements of childhood Robinia perseudoacacia are 420.3 and 506.7 mm,respectively.The minimum and suitable ecological water requirements of young Robinia perseudoacacia are 602.4 and 730.4 mm,respectively.