To investigate the seismic behavior of reinforced concrete (RC) columns with stay-in-place ultra-high performance concrete (UHPC) formworks, named URC columns for short, we selected different assembly methods and surface treatment methods of UHPC formworks as design parameters and carried out pseudo-static tests on nine URC columns and one RC column. The assembly methods of UHPC formworks were boltangle steel connection, bolt connection, and epoxy resin mortar. The surface treatment methods of UHPC formworks were natural surface, bubble film printing, and adding ribs. The pseudo-static tests were conducted to study the influence of different assembly methods and surface treatment methods on the seismic behaviors of the URC columns. Additionally, on the basis of the assumption of plane section, a formula was proposed to predict the eccentric compressive bearing capacity of the URC columns. Results show that the bonding surface between UHPC formwork and concrete core had no apparent damage before the peak load, indicating that the URC columns have good integrity. In particular, the URC columns connected by boltangle steel had no interface bonding failure even under the failure load. Compared with the traditional RC column, the ultimate bearing capacity, ductility, and energy consumption of the URC columns were increased by 6.4%43.3%, 11.4%48.7%, and 27.7%85.3%, respectively. Among the three assembly methods, the URC columns connected by bolt and angle steel had the highest bearing capacity and the most reliable connection. Finally, the results calculated by the proposed formula were in good agreement with the test results, which can provide reference for practical application.