<p>To investigate the seismic performance of reinforced concrete (RC) column with ultra-high-performance concrete (UHPC) formwork, three RC columns with UHPC formwork (abbreviated as URC columns) and one conventional RC column were fabricated. The influence of various assembly methods of UHPC formwork on the seismic performance of the specimens was examined through experiments. The assembly methods included bolt–angle steel connection, bolt connection, and epoxy mortar connection. In addition, a finite element model was developed to analyze the impact of various parameters on the bearing capacity and ductility of the URC columns. Finally, based on the plane section assumption, a method for calculating the bearing capacity of URC columns was proposed. The results showed that, at the final failure state of specimens, the joints of UHPC formwork connected by bolts and UHPC formwork connected by epoxy mortar showed noticeable damage. In contrast, the joints of the UHPC formwork connected with bolts–angle steel remained relatively intact. Moreover, the bearing capacity of URC columns with various connection methods exceeded that of RC column. Parameter analysis results indicated that as the strength of the normal concrete and the thickness of the UHPC formwork increase, the bearing capacity of URC columns gradually improved, while ductility decreased. Finally, the proposed calculation method effectively predicted the bearing capacity of URC columns, with the error between the calculated and experimental (simulated) values remaining under 20%. These findings suggest that UHPC formwork can significantly enhance the seismic performance of RC columns, making it a promising solution for improving the resilience of structures in earthquake-prone regions. Furthermore, the proposed calculation methods provide practical guidance for engineers to optimize the construction of URC columns in real-world seismic environments.</p>