This paper presents an indirect method to compute the optimal trajectory for cable driven robots (CDRs). This optimal solution is subjected to robot’s dynamics and joint flexibilities. Dynamic equations are organized in a closed form and are formulated in the state space form. A computational technique is developed for obtaining optimal trajectory in robot’s workspace to maximize allowable payload. The problem is formulated as a trajectory optimization problem, which fundamentally is a constrained nonlinear optimization problem. It solved by using Pontryagin′s minimum principle (PMP). The basic problem is converted to the Two-Point Boundary Value Problem (TPBVP) which is included the joints flexibilities. The results illustrate the effectiveness of the proposed algorithm due to comparison between flexible joint model and ideal model for a 6DOF cable robot.