Abstract: The required workspace of the bionic eye is firstly defined.According to the special requirement of its configuration, a method to determine structure parameters of SPM(spherical parallel mechanism),which utilizes the worst-case performance index as the optimizing target in required workspace,is presented.Consequently,the worse performance in certain positions as well as the appearance of singular Jacobian matrix,which always happen when taking the average performance index as the optimizing target,are avoided.In addition,the optimizing process is carried out in required workspace instead of reachable workspace for the sake of minimizing the optimization scope and circumventing the calculation of reachable workspace.Finally,the bionic eye with the optimized parameters meets the design requirements.