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In the rice planting area of Northeast China, the large amount of rice straw with low moisture content is tough to chop during harvest, and straw decomposed slowly under low accumulated temperature. However, the existing machines and tools still cannot better achieve straw return to the field. The suitable chopping state of straw returned to the field was proposed, which was 5~10cm tearing state. Combined with the shape of the chopped straw and the use of the existing machines and tools, a straw chopping device with two stages of agitation, sliding cutting and tearing was designed and assembled with the combine harvester. The key parameters of crushing process were designed by theoretical analysis. The single factor test showed that when the moisture content of straw was decreased from 69.77% to 29.34%, the chopping qualified rate and broken rate of straw were decreased by 6.44 pencentage points and 955 pencentage points respectively due to the change of dry matter content and bending strength, and the spread width was increased first and then decreased. With the increase of harvest speed, the chopping qualified rate and broken rate of straw was decreased significantly, and the width of straw was reduced by 0.22m. With the increase of shaft speed from 2100 r/min to 2850 r/min,the chopping qualified rate and broken rate of straw were significantly increased, and the width of straw was also greatly increased. The interval of the two-stage fixed knife was enlarged, the chopping qualified rate and broken rate of straw were increased slightly, and the change range of the scattering width was less than 0.11m. Orthogonal test showed that the effect law on chopping qualified rate and broken rate of straw caused by harvesting speed and the rotational speed was almost consistent. The chopping qualified rate and broken rate of straw caused by harvest speed and cutter shaft speed were more significant（P＜0.05). The spread width caused by cutter shaft speed and the interval of the two-stage fixed were more significant（P＜0.05). The design of the device was of great significance and application value to the key technical problems of straw returning in the rice planting area of Northeast China.