We develop a two-dimensional plane-strain viscoelastoplastic finite element model to simulate the evolutions of displacement, velocity, and strain across the Longmen Shan (LMS) fault Zone during seismic cycles. In this study, we investigate strain partitioning and seismicity in eastern Tibet due to purely crustal shortening, lateral variations in lithospheric viscosity beneath eastern Tibet, the increased lower-crustal flow velocity, and the active Longriba (LRB) fault. Our results show that the accumulated interseismic strain across eastern Tibet is released mainly by the characteristic large earthquakes on the LMS fault, leading to prominent coseismic uplift of eastern Tibet. During the postseismic period, eastern Tibet, especially the LMS region, continues to uplift due to viscoelastic stress relaxation in the middle–lower crust and upper mantle. When a stronger Ahba sub-block or middle–lower crustal flow is considered, the modeled vertical displacement and velocity in the upper crust increase largely in the LMS sub-block, causing more rapid uplift of this region. We also demonstrate that the active LRB fault would accommodate some crustal shortening, repartition the strain in eastern Tibet, and eventually change the seismicity on the LMS fault.