Poplar plantations are the most prevalent and the fastest expanding plantations in Northern China. However, the high water use of poplars necessitates careful consideration of their suitability for water-stressed regions. It is essential to find out the relationships between the water transpired by poplar plantation and environmental factors during different growing periods, which is very important in poplar plantation sustainable management. Many researchers have done a lot of job on this subject, but few referred to a mature fast growing poplar stand. In the current study the water use and response to environmental factors was evaluated by simultaneous measurements of sap flow using the TDP (Thermal Dissipation Probe) method, micrometeorological conditions and soil moisture in a 13-year old poplar (Populus euramericana cv. "74/76") plantation located on the floodplain of Yongding River in Daxing district, the southern suburb of Beijing, China from 2010 to 2011. Our objectives were to illustrate the water used for transpiration by this 13-year old fast growing poplar plantation and explore how the tree/stand transpiration responses to the different environmental conditions. The results showed that the daily pattern of sap flow was a bell curve. The daily water consumption of individual trees ranged from 6.4 to 59.7 kg/d, varying by season and sapwood which was calculated through the trunk diameter at breast height. On a ground area basis, the growing season transpiration was 114 and 175 mm in 2010 and 2011, respectively. It accounted for 30%-37% of precipitation over the same periods. Compared to earlier reports for poplars in literature, the observed water use was relatively low, likely attributable to growing age and no available irrigation during the study period. A diurnal hysteresis was observed between sap flow and vapor pressure deficit (VPD). Similarly, this situation was also true between sap flow and net radiation (Rn). The hysteresis was greater with high than low soil moisture, suggesting that transpiration did response to the change of soil moisture though indirectly. On daily scale, significant correlations were observed between daily stand transpiration and Rn, VPD and soil moisture. Besides, the relationship between transpiration and soil moisture was related to the depth of soil. The soil moisture under the surface 30-90cm affected transpiration most effectively. When the soil moisture changed, the relationship between stand transpiration and Rn or VPD varied. The growth of VPD stimulated the stand transpiration when it was not greater than 1 kPa. The over great value of VPD would slow down the growth of stand transpiration. Compared to the data of earlier research at this site, we found that the transpiration of the plantation declined with the stand age. On a monthly and annual scale, transpiration was correlated with rainfall, suggesting limited soil water storage. Simultaneously, we found that during dry months when transpiration could not be satisfied by rainfall, soil water storage offered the water to be transpired. However, the source of soil water storage was also come from rainfall thus the transpiration between 2010 and 2011 were quite different because of great rainfall difference in these two years.