The channel flow model was gradually being accepted with the more important multidisciplinary evidences from geology and geophysics, but how the lower crustal flow influenced the surface deformation quantitatively was unknown. Here, we develop a three-dimensional viscoelastic model to explore the mechanical relations between the lower crustal flow and the surface deformation in western Sichuan. Based on numerous tests, our results show that the modeled results fit well with the observed GPS data when the lower crust flows faster than the upper crust about 11 mm/a in the rhombic block, which can be useful to understand the possible mechanism of the surface deformation in western Sichuan. Moreover, taking the Xianshuihe fault as an example, we preliminarily analyze the relation between the active fault and stress field, according to the boundary constraints that deduced from the best model. The results show that the maximum shear stress on the Xianshuihe fault zone is mainly located in the fault terminal, intersections and the bend of the fault geometry, the stress level on the northwestern segment that has the high slip rate is relatively high. Additionally, with the reduction of the Young’s modulus in the fault zone, it’s conducive to generate the greater strain distribution, hence forming the high stress level. The channel flow model was gradually being accepted with the more important multidisciplinary evidences from geology and geophysics, but how the lower crustal flow influenced the surface deformation quantitatively was unknown. Here, we develop a three-dimensional viscoelastic model to explore the mechanical relations between the Based on numerous tests, our results show that the modeled results fit well with the observed GPS data when the lower crust flows faster than the upper crust about 11 mm / a in the rhombic block, which can be useful to understand the possible mechanism of the surface deformation in western Sichuan. Moreover, taking the Xianshuihe fault as an example, we preliminarily analyze the relation between the active fault and stress field, according to the boundary constraints that deduced from the best The results show that the maximum shear stress on the Xianshuihe fault zone is mainly located in t he fault terminal, intersections and the bend of the fault geometry, the stress level on the northwestern segment that has the high slip rate is relatively high strain distribution, hence forming the high stress level.