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The Tibetan Plateau (TP),a grouping zone for natural reserves,is significant for the human society sustainable development under global warming as well as anthropogenic activities,e.g.regional water balance,carbon cycle and engineering constructions.For the easy accessibility and available groundbased measurements,the Beiluhe,Qinghai,China is selected as the experimental site,locating in Hoh Xil National Natural Reserve.19 ALOS PALSAR images acquired with ascending orbit,from June 2007 to December 2010,are used in this study.The 3-arcsecond (~90 m) Shuttle Radar Topography Mission (SRTM) DEM data from the United States Geological Survey (USGS) are used for topographic phase estimation at the first step,and then for geocoding InSAR products (transforming Range-Doppler coordinates into Universal Transverse Mercator map geometry system).Considering the close relationship between the active layer motion and the permafrost evolution (degradation or extension),the Multi- Temporal SAR Interferometry (MT-InSAR) is introduced for surface movements surveillance.This innovative technique mitigates the intrinsic limitations of the traditional Differential InSAR (spatialtemporal decorrelation as well as atmospheric disturbance),resulting in millimetric accuracy using large datasets over the same scene.In order to minimize the seasonal decorrelation,the small baseline strategy is further applied; that is,the interferograms small than 3800 m spatially and 368 days temporally are firstly generated.After phase unwrapping,the classical Small Baseline Subsets (SBAS) (one of MTInSAR approaches) is employed for the surface velocity and displacement time series inversion.Using the two thresholds (0.4 average spatial coherence and 0.6 temporal coherence),surface velocity rates in Line Of Sight (LOS) over Beiluhe TP region are then derived.The corresponding values are primarily in the range of - 30 mm/yr to 30 mm/yr,revealing active motions during the 3.5-year observation period.In addition,we also find that InSAR techniques are promising for water level detection when the assumption of double-bounce refection holds,e.g.the dihedral scattering composed by the flat water and cliff shores.The conclusions of this study can be drawn as follows: 1)The surface motion of overlaid active layers in permafrost environment of TP is evident in the observation span,primarily in the range of -30 mm/yr to 30 mm/yr.2)MT-InSAR is potential for water balance estimation through the water level detection of inland lakes in TP.3)The Qinghai-Tibet Railway (QTR) and its neighborhood are suffering from much remarkable surface subsidence than surrounding features,implying the anthropogenic activity influences.