Abstract: In order to explore the reasonably afforestation density of Populus in western Jilin Province, we investigated water consumption characteristics of Populus simonii×P. nigra var. italica using stem sap flow determining system and environmental factors using automatic weather station. Results showed that the diurnal variation of different density poplars sap flux density presented a single irregular peak curve in sunny day of growing season, and had a good ecological synchronization with solar radiation temperature and wind velocity. Through the analysis of transpiration water consumption, rainfall and water use efficiency for each unit area, it can be initially confirmed that the planting density of poplar artificial forests ranging from 5 m×5 m to 6 m×6 m is reasonable.