Abstract: The characteristics of root growth in the fast-growing and high-yield plantations of I-214(Populus euramericana cv.‘I-214’) poplar under subsurface drip irrigation(SDI) and normal irrigation(NI) on sandy soil of Chaobai River in Beijing were studied.It is better to further research the fast-growing and high-yield mechanism of trees under SDI.The results showed that,compared with NI,there was a big increase in the amount of roots(d<10 mm)(especially that of roots(d<2 mm)) under SDI,such as the amount of roots(d<10 mm) under SDI was three times more than that under NI in the soil layer of 20-50 cm.It is one of the important reasons of increasing the productivity of the plantation increased.The absorbing roots under SDI were concentrated in the soil layer of 20-50 cm,while the roots under NI were distributed in each layer evenly.As roots(d<10 mm) distributed in level,those under SDI distributed mainly near the droppers and the amount of roots in 3 m in row under SDI was 50% less than that under NI.So it is suggested that droppers having the shape of "#" should be collocated in the middle of two rows and two individual trees in order to increase the distributing and absorbing range of root under SDI,and further increase the plantation productivity.