Abstract: It is universally acknowledged that phreatophytic transpiration changes sensitively with groundwater level de- clining. The present study tries to find the groundwater level decline threshold limited to the vulnerable ecological con- ditions at Yushen mine. The methods include in-situ test and numerical analysis,firstly an experimental base was con- structed for collecting data,including meteorological factors,soil moisture,groundwater level and Salix psammophila transpiration,then a root water uptake model was derived to simulate the change of Salix psammophila transpiration during groundwater level declining. The results show that:Salix psammophila transpiration is strictly controlled by me- teorological factors,there appears two extremums before and after 12 noon,and Salix psammophila transpiration chan- ges more sharply with a shallow groundwater level. The contribution rate of groundwater to evapotranspiration declines with the groundwater depth goes deeper,which decrease from 100% to 0 with groundwater depth decreasing from 15 cm to 215 cm. Salix psammophila cannot utilize groundwater when the groundwater depth is more than 215 cm,that is the threshold of groundwater level decline limited to the vulnerable ecological conditions during coal mining in the study area. The results achieved above will enrich the coal mining technology at ecologically vulnerable coal mine.