Abstract: The prestressed rocking steel bridge pier with external energy-dissipating components and base plate is taken as the research object. The geometric equations at each region of the bottom surface of the stiffened square-section rocking steel bridge pier were derived, and both the calculation formulae for the component internal forces under the horizontal cyclic loading and the analytical calculation method for the whole process of the pier were developed. The validity of the analytical calculation method proposed was verified by comparing the calculation results of the analytical calculation method and those of the refined finite-element model of the rocking steel bridge piers, and the variation law of the height of the compression zone with the pier generalized rotation angle was deeply analyzed. The results show that the geometric equation based on the generalized rotation angle and intercept strain can ensure the ideal transition of hysteretic curve before and after the critical depression point. The calculation results obtained from analytical calculation method of stiffened square-section rocking steel piers are in a good agreement with those obtained from the finite-element model. The static analytical calculation method proposed under horizontal cyclic loading of the rocking steel pier can quickly and accurately obtain the hysteretic performance of the rocking steel pier with given structural parameters. The hysteretic curves of the stiffened square-section prestressed rocking steel pier with base plate and external energy-dissipating components show the obvious flag-shaped characteristic, indicating that the new type of steel pier has good energy dissipation capacity and small residual displacement, which meets the seismic resilience requirement with recoverable function after earthquake. The analytical method proposed can obtain the history of the height of the compression zone with the generalized rotation angle of the rocking steel pier. The negative slope value of the curve will continuously decrease and may even appear positive in the rotation-angle-increasing section, while the slope is always negative in the rotation-angle-decreasing section and the height of the compression zone in this section is greater than that in the rotation-angle-increasing section. When increasing the axial compression ratio or the prestress degree, the compression zone–generalized rotation angle curve rises as a whole, but the influence of other parameters on the curve is small.