During the maize harvest, to increase the percentage of qualified length of stalk chopped and degree of stalk breakage to accelerate the decomposition rate after the straw being returned to the field, the device for chopping stalk was designed based on the mechanical properties of maize stalks and would make it be installed under the header of maize harvester. The working parameters and structural parameters affecting the working performance were obtained through the theoretical analysis. The rotational speed of shaft of chopper, fixed angle and tip angle of the blades were selected as the experimental factors. The percentage of the qualified length of stalk chopped and the percentage of the stalk broken were used as evaluation indexes. The quadratic orthogonal rotational-combinational tests were conducted. The experimental data were analyzed by the response surface method, and the multi-objective optimization algorithm of Design-Expert software was used to optimize the parameters. The results showed that the rotational speed of shaft of chopper had the most significant effect on the percentage of qualified length of stalk chopped, and then the tip angle, finally the fixed angle, and the rotational speed of shaft of chopper had the most significant effect on the percentage of the stalk broken, and then the fixed angle, finally the tip angle. The optimized parameters of the device for chopping stalk were the rotational speed of shaft of chopper of 1090r/min, the fixed angle of 41°, and the tip angle of 83°. The stalk-chopping device was produced. The field tests were carried out. The percentage of the qualified length of stalk chopped and the percentage of the stalk broken were 90.21% and 85.78%, respectively. The performance of the device for chopping stalk in working was much higher than that of the current chopper device below the header of harvester.