During the rolling process of big size parts, crinkle and hollows often appear in the surfaces. The reason of producing the defects is that the motions of the rolling mill tool are not consistent with the deformation of the part. On the basis of the principle of radial-axial ring rolling, a dynamics model is put forward. The relationship between part deformation and motion parameters is set up. The stress and strain of the part are simulated in the Finite Element Method by DEFORM software. A ring rolling process curve is defined. The rolling process is controlled by the curve. It is able to make the deformation of the part be consistent with the process parameters, and improve the product quality.