On January 7, 2025, an MS 6.8 earthquake occurred in Dingri County, Xigaze City, Xizang Autonomous Region. It is the largest seismic event in the southern Tibetan Plateau since the 2015 Nepal earthquake. Owing to the high-altitude environment and sparse coverage of strong-motion and GNSS stations in the epicentral area, traditional seismological methods have limited capability in constraining the rupture process. To accurately determine the seismogenic structure and slip distribution of this earthquake, C-band Sentinel-1 and L-band ALOS-2 descending SAR images were jointly used. High-precision coseismic deformation fields were obtained based on Interferometric Synthetic Aperture Radar (InSAR) technology. Quadtree downsampling and the elastic half-space dislocation model were adopted for fault inversion. To reduce subjectivity in fault geometry parameter searching, the central focal mechanism solution method was introduced. Multiple focal mechanism solutions from different institutions were integrated to improve the objectivity and reliability of parameter constraints. The inversion results show that the earthquake is a shallow normal-faulting event with a minor left-lateral strike-slip component. The seismogenic fault strikes nearly north–south (186.3°) with a dip angle of about 54°, a length of about 30.5 km, and a width of about 10.2 km. Rupture is mainly concentrated at depths of 3.4–14 km, and the maximum slip reaches about 4.3 m at a depth of about 6 km. The modeled deformation agrees well with the InSAR observations, which verifies the reliability of the fault model. The results provide important constraints on the present tectonic deformation, crustal stress state, and strain partitioning mechanism in the southern Tibetan Plateau. They also provide a scientific basis for seismic hazard assessment and earthquake disaster mitigation in the southern segment of the Shenzha–Dingjie Rift.