In this paper, equivalent dynamic infinite element is proposed. The idea of the method is based on the elastic recovery of general infinite element and the energy absorption of viscous boundary. The equivalent dynamic infinite element is not required for wave functions, since the waves on the interfaces with adjacent finite and infinite elements are absorbed by the equivalent damping. And the role of the far field medium in the elastic recovery has also been considered in the equivalent dynamic element. Such an element can be used directly as general finite element and appropriates for dynamic soil–structure interaction problems. Numerical analyses involving comparisons with known analytical or numerical solutions are presented. The results obtained show the effectiveness of the proposed equivalent dynamic infinite element.