In order to ensure the safety and reliability of the structural connection of assembled bridges, the strength test design of different types of interface agents was carried out based on bridge engineering and structural mechanics, and the mechanical properties of different cement grades, water-cement ratio and ash-sand ratio were analyzed. The change law of the strength of cement mortar in the early stage is faster than that in the later stage. The change law of the compressive strength of different types of interface agents with different ages was obtained, the prediction model of the relationship between different ages and strength of cement mortar was constructed, and the optimal mechanical properties of SS-Ⅲ were proposed from the perspective of the bending-compression ratio. The relationship between different interface agents and the tensile strength of adhesion splitting was tested and analyzed by developing the test device of adhesion splitting tensile strength. The bonding performance of SS-III was determined to be the best interface bonding agent for assembled bridges from the perspective of the bending ratio and bonding properties. cement mortar as the interface agent for assembled bridges is more reasonable, which provides a new research idea for the safety and reliability analysis of the interface connection of assembled bridges.