<p>Investigating the lateral distribution of lithospheric rheological structures based on post-seismic deformation is scientifically significant for advancing our understanding of tectonic deformation mechanisms. This study integrates GNSS and InSAR observations to extract three years of post-seismic deformation following the 2021 Mw 7.4 Maduo earthquake. Based on the GNSS and InSAR observations, we separate the contributions of after-slip and viscoelastic relaxation. First, the initial after-slip distribution was inverted from InSAR data. Then, the magnitude of after-slip was constrained with near-field GNSS data. Finally, far-field GNSS observations were used to infer the viscosity of the lower crust. Simulations indicate that the optimal steady viscosity near the source region in the Baryan Har Block is approximately 3 × 10¹⁸Pa·s—an order of magnitude lower than that of the Qaidam Block to the north. After accounting for viscoelastic relaxation, after-slip is primarily concentrated in the elastic upper crust (above 30&#xa0;km depth). Over the three-year period, the after-slip has released a cumulative seismic moment of 1.343 × 10¹⁹ N·m (Mw≈6.69), accounting for approximately 7% of the co-seismic moment. Post-seismic deformation during the 3–6&#xa0;years following the mainshock predominantly affected crustal deformation in the Bayan Har Block between 96°E and 101°E. Consequently, when analyzing the inter-seismic slip behavior of faults in this region, the effects of post-seismic deformation from the Maduo event must be carefully removed.</p>