In order to solve the interface bonding problem between new and old concrete involved in the maintenance and reinforcement of existing structures and the construction of prefabricated buildings, this paper studies the interface bonding problem between high-strength ultrahigh performance concrete (UHPC) and normal concrete as the bonding material. On the basis of considering two factors, interface roughness and concrete strength, this article conducted direct shear tests. The test results showed that improving both concrete strength and interface roughness can improve the interfacial bonding performance between the two, but the influence of interface roughness is more significant; The specimen using a Type III interface experienced cracking in the UHPC layer during failure, but the failure did not occur at the interface. Its interface adhesion is better, and it can reliably transmit force. Therefore, in practical engineering, this article recommends using a Type III interface. Afterwards, a finite element model of the plug-in single column pier was established, and the calculation results showed that the influence of concrete strength on the bearing capacity of the bridge pier was greater than that of interface roughness, but it more affected the strength of the bridge pier, while interface roughness changed the bonding performance of the interface. At the same time, the influence of interface roughness on the bearing capacity of bridge piers made of low-strength grade concrete is more significant. Therefore, increasing interface roughness can be used to improve the stress performance of low-strength concrete bridge piers and ensure their integrity.