Applicability of the simplified method based on equivalent single-degree-of-freedom (ESDOF) for single-column pier with uniform cross-section is investigated in this paper. The modal participating mass ratio of pier’s fundamental mode is taken as an index to evaluate the applicability of the simplified method. Based on the fundamental mode shape functions selected deliberately in the first step, equations to evaluate the modal participating mass ratio of pier fundamental mode is obtained. Using the proposed equations, it is convenient to evaluate applicability of the simplified method with the height of the pier and the ratio of the linear mass along the column to the dumped mass at the top of the pier. Finally, the index is verified in the different nonlinear range of piers.