For a given set of motion input parameters, the parallel manipulator is possibly at the states of configuration bifurcation. In order that the parallel manipulator can move at will when the lengths of links changed in determinate regions, we optimized the mechanism by considering configuration bifurcation. Based on the idea of analyzing the movement state of parallel manipulator in link space, sixteen kinds of extreme poses for 6-DOF parallel manipulator were described with the vector expressions of link lengths. In order to avoid configuration bifurcations, the bifurcation characteristics of extreme poses were analyzed by homotopy method and static bifurcation condition. The kinematic controllable condition of the designed manipulator was analyzed, which makes the manipulator controllable in the length area of links.