Cold ring rolling is a kind of advanced manufacturing technology. During rolling process the ring may be collapsed or deformed unexpectedly under the pressure of guide roll because the stiffness condition is not met. The force of guide roll to ring was obtained by analyzing the forces to ring. The stiffness condition expressions of ring during rolling were shown after constructing the mechanical model. According to the expressions, the effects of several parameters on the stiffness condition were discussed and analyzed in detail, such as position angle of guide roll, friction coefficient and feed rate, etc, which revealed essential reasons of some cases occurring in cold ring rolling. Then the ring blank dimension was deduced based on the ring stiffness condition. The dimensions of ring blank should meet a relationship to ensure the ring stiffness condition to be satisfied during rolling, which can conduct the practical manufacturing effectively. Finally the analysis and effect laws were proved by finite element simulation experiments. The researches could be helpful to control parameter in cold ring rolling effectively for high quality products.