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In order to improve cleaning performance of cross airandscreen cleaning device in maize harvester, through comparing the screening performance of woven screen and shell screen, the structure of shell screen was selected as the main object of study. In order to obtain the optimal parameters of the shell screen, computational fluid dynamics and discrete element method (CFD-DEM) were coupled in the quadratic orthogonal rotationalcombinational simulation tests. Objective indexes were screening efficiency of shell screen and cleaning rate of grain. The factors were the length and height of screen hole and the space between screen holes. The test data were analyzed by the response surface method and the regression mathematical models were multiobjective optimized by using Design-Expert software. Simulation results showed that height of screen holes had the most significant effect on the indexes, followed by the space between screen holes, then the length of screen holes. The optimized parameters were the length of screen hole of 21.68mm, height of screen hole of 10.86mm and space between screen holes of 55.04mm. The results of verified test showed that screening efficiency was increased from 81.79% to 89.91% and the cleaning rate of grain was increased to 9728%, which were consistent with the simulated results. The performance of the cleaning device was enhanced.