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Most of cleaning devices in maize harvester are parallel-mounted double screen. In order to improve the screening performance of the double screens, a four DOF double-layer non-parallel vibrating screen mechanism and test bench were designed by using the bias crank slider mechanism. The mathematical model of mechanism motion was obtained by using matrix analysis method. The results showed that the sieve movement was non-harmonic periodic motion. The factors were the installation spacing of double screens, the mounting inclination of upper screen, and the transverse amplitude of screen. The indexes were the loss and impurity rate of maize. The test data were analyzed by the response surface method and the regression mathematical models were multi-objectively optimized by using Design-Expert software. When the mounting inclination of lower screen was 3.5°, the optimal parameters were the installation spacing of double screens of 292.99mm, mounting inclination of upper screen of 3.04°, and transverse amplitude of screen of 5.55mm. Test of driving mechanism size was done based on optimized parameter adjustment. Under the condition of the normal feed quantity of maize mixture of 5.05kg/s,the loss rate of grain was 1.61% and the impurity rate of grain was 2.17% after screening, which can meet the performance requirement of maize harvester. Compared with the traditional double plane reciprocating vibrating screen cleaning device, the loss rate of grain was reduced by 1.59 percentage points.