Abstract: In this paper, the soil moisture sensors were adopted to study the dynamics of soil volumetric water content (SVWC) in poplar plantation cultivated with ground drip irrigation system at ancient sandy land of Yongding River in Beijing. The changing process of SVWC was measured under condition of various time lengths of drip irrigation treatments with eraser of consistent rate of flow in 4 L/ hour, in order to illustrate the quantitative relations of SVWC and different time lengths of irrigation and post irrigation. The study showed following results and conclusions: 1) During the continuous drip irrigation of 6 hours, the changing process of SVWC at most testing locations appeared a tendency of fast increase to slow increase and then remaining stable. 2) After continuous drip irrigation of 1.5, 2.5 and 5.5 hours, the SVWC will increased over the field water capacity (FWC) at testing location of 20, 30 and 40 cm apart from eraser horizontally in soil of 20 cm deep respectively, while after continuous drip irrigation of 2.5 and 4.5 hours, SVWC increased over FWC at the testing location of 0 and 20 cm apart from eraser horizontally in soil of 40 cm deep respectively. 3) After drip irrigation of various time lengths, the SVWC appeared a tendency of fast decrease to slow decrease if SVWC reached the maximal value when irrigation stopped, while the SVWC appeared slow decrease consistently if SVWC reached the maximal value when drip irrigation stopped for 6 hours. 4) After continuous drip irrigation of 2, 3 and 5 hours, the SVWC will remain over 80% FWC in 48 hours after stopping irrigation at the testing location of 20, 30 and 40 cm apart from eraser horizontally in soil of 20 cm deep respectively, while after continuous drip irrigation of 3, 4 and 6 hours, the SVWC will remain over the 80% FWC in 48 hours after stopping irrigation at the testing location of 0, 20 and 30 cm apart from eraser horizontally in soil of 20 cm deep respectively. The above mentioned study conclusions will provide necessary theoretical basis and technical references for designing and running the ground drip irrigation system to cultivate high-yielding tree plantations in the ancient sandy land of river.