Abstract: A hulling device was designed and optimized based on the physical characteristic of castor capsule in order to increase hulling rate and decrease breaking rate. A mathematical model of force and deformation was proposed. The relationship among extrusion pressure P, rolling angle, roller deformation ΔR, clearance between two rollers, diameter of castor capsule and diameter of roller were obtained by MATLAB calculation. Results showed that rotation rate of rollers, clearance between two rollers and rate differential between rollers were main factors to the castor capsules' hulling. The final optimized parameters for the best hulling rate were rotation rate at 10 r/min, clearance between rollers 18 mm, rate differential 30 r/min, while factors combination of optimizing breaking rate were rotation rate 10r/min, clearance between rollers 12 mm, rate differential 30 r/min. And the optimized parameters for the best breaking rate were rotation rate at 10r/min, clearance between rollers 12 mm, rate differential 30 r/min. This research provides a reference for relative hulling device design and mechanism analysis.