The guiding roll is an important part of the ring rolling equipment which plays an important part in stabilizing the rolling and ensuring the quality of product. This paper obtained the formula for instant diameter of ring during the rolling process and established the motion equation of guiding roll. The angular velocity, instant displacements in X and Y direction of guiding roll center were calculated by MATLAB software. The numerical simulation of ring rolling of ring with rectangular cross sections was completed under the ABAQUS/Explicit environment after importing the instant displacement of guiding roll center. The simulation results indicate that the guiding roll could be controlled accurately by the proper method. These research conclusions can provide scientific basis for ensuring the quality of product and accurately controlling the movement of guiding roll during the ring rolling.