The cost of development for physical prototypes of parallel robots is high and the optimization cycle is long. The optimum method of high efficiency is explored. A virtual prototype model of 3RPS is established to analyze how the rotational angle of the robot is affected when the parameters of the robot vary. The results show that it is a good method and easy to be used in practice. The optimum parameters are obtainned for the workspace indicating that rotational angle is the best one.