Abstract: We focus on the dynamic modeling and cable tension optimal distribution for high-speed long-span cable-driven parallel robots with redundant actuations. Firstly, the dynamic model of the cable is established with the aid of the ideas of the finite-element method; secondly, the dynamic equation of the robots considering the cable dynamic is derived; then, a tension distribution optimal model suited for the robots is gained taking the minimum variance of the tensions as the objective function; furthermore, an iterative algorithm is proposed to determine the tensions optimally, which takes the cable tensions and lengths, obtained by a straight line model, as the iterative initial values as well as the unchanged sags of cables as the terminating condition. Consequently, the optimal tensions are determined. Finally, the necessity of considering cable mass and inertia effects is shown through a simulation example, and the convergence, effectiveness and rationality of the algorithm are verified, laying a theoretical foundation for force control to cable-driven parallel robots.