In view of the existing fresh corn harvester in grain harvest, grain contains impurities such as stem leaf, affected transportation, storage and subsequent processing and so on, by axial flow fan technology of negative pressure to get rid of the impurities such as the stem and leaf of ear, at the same time increase in the subtraction, knife chop of impurities, facilitating subsequent packaging recycling. Performance analysis and parameter optimization were carried out for the fan negative pressure impurity removal device, in order to reduce the rate of clutter in the ear and improve the recovery efficiency of green stalks. Through the dynamic analysis of moving and fixed knives, as well as the analysis of the number and clearance of moving and fixed knives, the fan speed range of the device was determined to be 1326~1573r/min, the clearance of moving and fixed knives was 20mm, and the fixed knives were 3~8. Using quadratic regression orthogonal combination experiment schemes to the fan speed, knife number, feeding amount as test factors, chop to grain impurity rate and stem length, percent of pass was bench test, the test indexes were obtained by analysis of the contribution rate of various factors on the indicators qualified rate of the primary and secondary influence stem chopped length in order to feed rate, the fan speed, the number on the edge of the sword. The primary and secondary order influencing the impurity rate of fruit ear were fan speed, feeding amount and fixed number of knives. The mathematical model of parameter optimization was established, and the optimization module was used to get that when the fan speed was 1524r/min, the single setting knife was 4, and the feeding amount was 7.6kg/s, the qualified rate of the cutting length of the stalk was 96.8%, and the hybrid rate of the ear was 0.69%. When the fan speed was 1524r/min, the number of fixed blades was 4, and the feeding amount was 7.6kg/s, the qualified rate of cutting length of stalk was 96.2%, and the impurity rate of ear was 0.71%, which was 23.3% lower than that of traditional harvester. The experimental results showed that the optimized parameters met the technical requirements of fresh corn ear harvest and stem and leaf silage.