Aiming at the on-orbit assembly of large-scale trusses in space， an on-orbit assembly system for space trusses is designed， including an assembly robot and a truss system based on component-level modular units. Considering the safety and orderliness of the whole assembly process， a mathematical expression of the truss rod assembly process based on the adjacency matrix is constructed， which is used to plan the assembly sequence of each rod of the cubic truss unit. At the same time， an arc trajectory planning method for arbitrary assembly positions is proposed to ensure the smoothness of the whole process of rod assembly and the positive alignment in the docking stage. Finally， an adaptive smoothing control algorithm that dynamically adjusts the parameters according to the contact force is utilized to ensure the safety and smoothness of the truss rod contact assembly. Based on the joint simulation model of ADAMS and Simulink for space truss on-orbit assembly system constructed in this paper， it is shown that the autonomous assembly trajectory planning and control strategy proposed in this paper can realize the autonomous smooth and compliant assembly of space truss， and the contact force in the assembly process is less than 10 N.