In traditional hulling machine, The lower of shelling rate and higher of breakage rate of castor. The self-designed hulling machine is adopted in this issue to study the prosess of capsule hulling. By analyzing the state, As gap between rollers reaches the minimum space, distortion from capsule to roller surface reaches the maximum, as the same as both the pressure of roller surface on castor-oil plants P and friction force F which indicates the strongest effect of extrusion and rubbing. the required condition of capsule rolling is that the angel of rolling（ ） should be no larger than frictional angel of roller（ ）. The highest shelling rate and lowest of breakage rate can be gained by using a steel matrix roller coated by plastic with 10r/min rotation rate of rollers and 18mm gap between rollers.