Abstract: This study presents a three-dimensional viscous-spring boundary element based on the mass-proportional damping. The damping coefficients are derived by using the principle of element matrix equivalence. Compared to the traditional viscous-spring boundary element using the stiffness-proportional damping, the proposed element maintains the explicit format of the conventional central difference method due to the diagonal damping matrix. Numerical stability analysis indicates that the explicit numerical stability of the viscous-spring elements proposed is slightly superior to that using the stiffness-proportional damping. Taking the three-dimensional the Lamb problem and the endogenous excitation problem of an arch dam-reservoir-foundation system as examples, the calculation accuracy of the three-dimensional viscoelastic boundary element proposed is proved.