The discrete element simulation of seed crushing in the rapeseed combined harvester and optimization of shredding and throwing device were conducted to solve the problems of increased operational losses caused by the breakage of rapeseed seeds during the shredding and throwing process of the self-developed rapeseed combined harvester. A rapeseed seed bonding model was constructed based on discrete element method and uniaxial compression tests were carried out. The optimal combination of parameters for rapeseed seed bonding model was calibrated through the steepest climbing experiment and Box-Behnken experiment. A simulation model of the shredding and throwing device for the rapeseed combined harvester was established based on the rapeseed seed bonding model. Box-Behnken experiment with three-factor and three-level was conducted with the rotating speed of the drum， the shredding clearance and the number of cutters as experimental factors to determine the optimal combination of parameters for the shredding and throwing device. Bench experiment and field experiment of the rapeseed shredding and throwing device were performed as well. The results showed that the simulated value of rapeseed seed crushing load was 12.67 N， and the relative error with the physical value was 3.59% when the normal stiffness coefficient， tangential stiffness coefficient， critical normal stress， and critical tangential stress was 7.0×10⁹ N/m， 6.82×10⁹ N/m， 6.61×10¹⁰ Pa， 8.18×10¹⁰ Pa， respectively. The optimal combination of parameters for the shredding and throwing device was a rotating speed of the drum of 450 r/min， a shredding clearance of 30 mm， and 10 cutters. The crushing rate of rapeseed seeds in the shredding and throwing device showed a trend of linear increase with the increase of the rotation speed of the shredding drum. The average crushing rate of rapeseed seeds in the shredding and throwing device for the rapeseed combined harvester was 0.82%， and the operation of the shredding and throwing device was smooth. It will provide a reference for the improvement and optimization of the structure of the shredding and throwing device for the rapeseed combined harvester.