[Objective] The influences of environmental factors on sap flow rate of Populus euphratica were analyzed to provid method data base for the calculation of water consumption by natural vegetation in arid area.[Methods] The trunk sap flow of Populous euphratica at the lower reaches of Tarim River was measured continuously during the whole growth season in 2012 and its responses to environmental factors were analyzed.[Results] The sap flow of Populus euphratica presented an unimodal curve, with obvious day and night variation rhythm. During the growth season, the relations between sap flow rate and environmental factors depended upon the temporal scales. Regress analysis showed that when observed at less hour scale, sap flow were associated closely with air temperature and soil temperature at depth of 10 cm. However, on daily scale, solar radiation was the major influencing factors; and on monthly scale solar radiation and air temperature were the major influencing factors.[Conclusion] The major factors assocated with sap flow of Populus euphratica are air temperature and solar net radiation, and the regressions of them with the sap flow rate were fitted wells.