In order to study the effect of screw extrusion mechanism on the dewatering efficiency of food waste, a micro element discrete model connecting material characteristics and screw extrusion device parameters was constructed, combined with numerical simulation, the four factors affecting the dehydration efficiency of the unit, such as the initial moisture content of materials, the filling degree of materials, the form of spiral blades and the spiral speed, were theoretically calculated. In the process of building the model, the parameter scheme with relatively optimal dehydration efficiency was selected by using the analysis method of orthogonal test. The conclusion provided a theoretical basis for the design and selection of screw extrusion mechanism. The calculation results showed that the screw speed and material filling degree had a significant impact on the dehydration efficiency of the unit, and the maximum dehydration rates were up to 40% and 40.6%. The initial moisture content of materials and the form of spiral blades had little influence on the dehydration efficiency of the unit, and the maximum dehydration rates were only 16.6% and 14.8%. The orthogonal test results showed that the moisture content at the end of the material was 69.7% for variable pitch helical blade structure, under the condition that the initial moisture content of the material was 80%, the material filling coefficient was 75%, and the screw speed was 15 r/min. Considering the factors such as energy consumption, work efficiency and cost performance, the parameter condition had the most advantages in the actual working conditions.