In order to improve the thresh efficiency of maize pair seeds and reduce the percentage of damaged seeds, experiments were carried out about the maize pair seeds thresher. The variety of maize was Meiyu No.3. The quadratic orthogonal tests were used. The effect of average water content, maize ear average diameter, thresher drilling tool diameter and drill angle on thresh percentage of pair seeds and damaged seeds of maize was analyzed. The mathematical model was developed. Taken the highest thresh percentage of pair seeds and the lowest percentage of damaged seeds as an evaluation index, the optimal parameters of thresher were obtained through multigoal nonlinear optimizing method. When the average diameter of maize ear was 39mm, the ear water content was 44%, the drilling tool diameter was 23mm and its angle was 74°. When the maize ear average diameter was 42mm, the ear water content was 44%, the drilling tool diameter was 24mm and its angle was 72°. When the maize ear average diameter was 47mm, the ear water content was 44%, the drilling tool diameter was 25mm and its angle was 70°.