This paper firstly analyzes the features of the spring-loaded type guide mechanism of D51 series vertical ring rolling mill. Then a reliable parametric virtual prototyping model of the guide mechanism is developed in software ADAMS. In addition, the optimal design of the guide mechanism is conducted. The minimum spring force is selected as the objective function, the dimensions of the parts of the guide mechanism are set to the design variables and the working condition is taken as the design constraints. The optimal guide mechanism is obtained after optimization, compared with the original structure, the spring force is decreased by 50.5%, and the guiding force is also decreased to a reasonable value. The research results can help to design the guide mechanism of the D51 series vertical ring rolling mill.