Seabuckthorn plant flexible dam is a new biology project used in preventing soil erosion and sediment retention and conservation of water in gully, especially in soft rock region with serious environment. An experimental research in field on sediment retention and water conservation of seabuckthorn plant flexible dam is carried on in the small east-one-branch gully of the representative soft rock region in Zhun-Ge-er county in inner Mongolia. It is showed by the results that the flexible dam can strikingly regulate soil water in the gully channel,and the spatiotemporal dynamic change is obviously different in distribution of soil water in soil profile in different positions of seabuckthorn plant flexible dam in a year and several years,and the important factors affecting spatio-temporal chang of soil water are rainfall,categories of vegetation,growth status of vegetation,physical and chemical characteristics of soil,terrain and hydrology whether condition of local region etc. , while rainfall and condition of vegetation in gully channel are mainly affecting factors among those.