To improve the seismic performance and construction fault tolerance of prefabricated assembled piers, this paper proposes a new connection method for assembled piers: assembled piers connected with ultra-high-performance concrete (UHPC) around piers. A cast-in-place bridge pier specimen and an assembled pier specimen connected with UHPC around the pier were designed and fabricated. A quasi-static test was performed on two specimens, and a three-dimensional solid nonlinear finite element model of the assembled pier specimen was established. The seismic performance and associated influencing factors of the proposed assembled pier were analyzed by performing a numerical simulation. The results showed that the assembled pier specimen connected with UHPC around the pier exhibited a similar lateral performance and self-resetting capability as the integral cast-in-place pier, and their seismic performances were the same. The fitting degree between the hysteretic curves of the nonlinear finite element model and the actual pier specimen was high, verifying the reliability of the modeling method and the accuracy of the simulation results. The height of the UHPC connection had little influence on the seismic performance of the assembled pier, and only the lap length of the reinforcement needed to be ensured. The axial compression ratio, column height, and lapped reinforcement ratio had evident effects on the seismic performance of the assembled bridge pier. When the axial compression ratio was between 0.1 and 0.3, the stiffness and horizontal bearing capacity of the specimen increased with the increase in the axial compression ratio. When the column height increased from 2.0 m to 2.5 m, the horizontal bearing capacity and accumulated hysteretic energy dissipation of the assembled pier decreased with the increase in the column height; when the reinforcement ratio was increased from 1.01% to 1.57%, the horizontal bearing capacity and residual displacement of the assembled pier were evidently improved compared with those of the original specimen.