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Aiming to increase the carrying capacity of maize cleaning sieve to high feed quantity to meet the requirement of rapid development of maize grain harvester. Through the analysis of mechanism of shellfish screening, the screening performance and the model of maize screening were obtained. In order to increase the probability of grain permeation, based on the screening characteristics of shell sieve and round sieve, the maize combined sieve which consisted of the shapes of shellfish and round hole was designed. Under the conditions of different feeding quantities of maize extractives, the simulation tests which included combined sieve, single round hole sieve and single shellfish screening test separately were carried out, then their screening performances were compared and analyzed. The results showed that compared with the single round hole sieve and the shellfish sieve respectively, the loss rates of maize of combined sieve was decreased by 4.79 percentage points and 7.85 percentage points when the feeding quantity was 5kg/s, the loss rates of maize of combined sieve was decreased by 5.79 percentage points and 7.84 percentage points when the feeding quantity was 6kg/s. Under the condition of feeding quantity was 2~6kg/s, the cleaning rate and sieving time were 99.22% to 97.53% and 4.87s to 5.50s partly, thus all indicators met the national standards. The performance of the combined sieve was verified by bench test. The loss rate of maize, cleaning rate of maize and screening time of the combined sieve were 1.09%, 95.94% and 6.48s, when feeding quantity was 6kg/s, respectively. Compared with the stepped sieve, the combined sieve grain loss rate was reduced by 5.60 percentage points, the screening time was shortened by 0.93s, and the performance of the cleaning device was further improved. 