Aiming to address lack of accurate modeling in discrete element simulation analysis for cleaning devices in combined oil sunflower harvest, the combined-harvested oil sunflower extracts were taken as object. A discrete element method was used to categorize and calibrate contact parameters for various oil sunflower extract models. The randomly selected oil sunflower extracts were classified, its main components were identified, and the corresponding mass fractions were determined using digital calipers, a universal testing machine, and a custom test platform measure intrinsic and contact parameters of each oil sunflower extract. Plackett-Burman, the steepest ascent, and Box-Behnken tests were proceeded based on each extract’s physical repose angle. Parameters with significant effects on extract repose angle were identified and their valid ranges were defined. An optimization module in Design-Expert software was employed and physical repose angle of each extract was treated as the objective value. The optimal parameter sets were determined as follows: oil sunflower seed shear modulus was 7.35×107Pa, oil sunflower seed-steel restitution coefficient was 0.295, oil sunflower seed-oil sunflower seed static friction coefficient was 0.669, crushed oil sunflower head shear modulus was 1.94×107Pa, crushed oil sunflower head-steel restitution coefficient was 0.467, crushed oil sunflower head-steel static friction coefficient was 0.436, oil sunflower stalk shear modulus was 7.39×107Pa, oil sunflower stalk-steel static friction coefficient was 0.553, and oil sunflower stalk-oil sunflower stalk static friction coefficient was 0.775. Simulation stacking tests were conducted on oil sunflower seeds, crushed oil sunflower heads, stalks, and mixed extracts based on each optimal parameter set. Results showed that errors between simulated and physical repose angles were 0.66%, 0.96%, 0.64% and 1.15%, respectively. These findings can serve as a reference for discrete element simulation research of combined oil sunflower harvest.