Through dynamic simulation of the cross-hinge four-bar mechanism, it is found the primary reason for unbalance of Sling the mechanism results from the unequal swing angle of driving link and driven link.To simplify analysis and calculation, a spatial switching approach was proposed to switch nonlinear problem into linear problem, by switching the problem of unequal swing angle of driving link and driven link into the problem of length variation of connecting link.Therefore, the length of driving link, the degree of its angle of intersection, and the amplitude of swing are three important parameters that influence the dynamic balance of the mechanism.An optimal design software was designed on the basis of establishment of target function and constraint conditions.Finally, through optimal calculation of the design software and Adams simulation, a Bracelets case was employed to test the efficiency of the optimal design approach.