A type of three DOFs cable-driven parallel mechanism was proposed, it contained three sets of cables, the same set of parallel and different sets of cross-structured cable branch chains and a set of passive elastic branch chains, which had the characteristics of light weight, high acceleration and large working space. Firstly, based on the closed vector method, the motion analysis of the mechanism was carried out to get the effect of spring branch chain on its working space. Secondly, the balance equation of the mechanism was derived based on the D'Alembert principle, and the relationship between the structural parameters of the intermediate elastic branch chain and the cable driving force was established by using the boundary search method and the controlled variable method to ensure that the mechanism met high acceleration and task working space. Taking the driving force of the rope as the optimization goal to optimize the structural parameters of the elastic branch chain, and determine the reasonable spring coefficient and initial length. Then, Lagrangian method was used to establish the dynamic equation of the mechanism, through the joint Matlab numerical calculation and ADAMS simulation to verify the correctness of the dynamic equation. Finally, the experimental sample was made based on the optimization results, and the institutional motion equation was verified by the experiment.