With the increase of the deployable length and the complexity of a space folded truss, the time cost of the numerical analysis on the deployment dynamics of the space truss system is increasing.In order to reduce the number of system generalized coordinates, the relative coordinates of joints were selected as system generalized coordinates, and the dynamic model for the folded truss of a space diffraction telescope during its deployment process was established based on the forward recursive formulation.The Jourdain’s velocity variation principle was employed to derive the variational equations of a single flexible body, and then the kinematic recursive relationship and the constraint equations of the cut joints were used to derive the rigid-flexible coupled dynamic equations of the system.In addition, concerning the numerical problem arising in the period of locking flexible components, a variable topology method was proposed, in which relative angle constraints were added on the revolute joints after the rotating speed was significantly reduced by damping torques.Based on the dynamic model, the numerical simulation and analysis of a folded truss system with 11 truss elements were carried out.In order to further reduce the time cost, according to the symmetric characteristics of the structure and the uniform distribution of the load in longitudinal direction, the deployable system, composed of multiple trusses and main mirror, was simplified to a single truss attached with a part of the main mirror.The correctness and effectiveness of the simplified method were verified by comparison of the simulation results with those obtained by the complex model.Finally, a folded truss system with 30 truss elements was analysed accordingly.The dynamic performance of the flexible truss in the process of deployment and locking was compared with that of the rigid truss system and the effect of the elatic deformation was analyzed.