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We present a multiscale decomposition model for analysing the widespread deformation and complex dynamics mechanism of the southeastern margin of the Tibetan Plateau. We first carry out simulations to test the performance of the model by synthetic Global Navigation Satellite System (GNSS) data for a network, whose geometry distribution is same with actual Crust Movement Observation Network of China in the southeast edge of the Tibetan Plateau. We then estimate the multiscale velocity field and strain rate field using observed data with 240 stations between 1999 and 2007. Results show that the deformation field at the different spatial scale corresponds to the different tectonic driving force and strain accumulation coverage. Tectonic background of the Tibetan Plateau, extrusion of the Sichuan–Yunnan rhombic block, rigid block motion, interior deformation of the block and segmented motion of fault zones are separately displayed in the corresponding scale, which provides a strong support keys to the understanding of the controversial deformation models for the tectonic evolution and uplift mechanisms of the Tibetan Plateau. Our results also show that scale 7 with the coverage of about 50 km can better reflect the seismogenic background of mid-strong earthquakes (> M s 5.0) of the region. The convergence area of high compression and inflation strain or the high-value area of maximum shear strain at scale 7 is obviously correlated with seismic activities, including 2008 Wenchuan M s 8.0 earthquake, no significant pre-seismic deformation across fault in other scales. Our research provides a new insight into the nature of tectonic deformation and the seismic risk assessment of the southeastern margin of the Tibetan Plateau. [ABSTRACT FROM AUTHOR]