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In the middle and lower reaches of the Yangtze River, the rice and rapeseed are the most important crops. They are planted in turn, and after the rice is harvested, rapeseed will be planted in time. High-efficiency combined precision seeder is often used to plant the rapeseed, which could complete seedbed preparation, ditching, fertilizing and sowing at once. However, here is a difficulty left by the previous rice harvest that is the harvest machine threshes the grain and leaves the rice straw in the field. The straw is easy to entangle the soil-touching parts of the combined precision seeder to block the machine, as well as the seeds are easy to fall on the straw, and difficult to emerge. Considering the kind of agronomic practice of straws covering for rapeseed cultivation, an innovation mechanized operation scheme both suitable for rapeseed seeding and returning rice straw mulch to the seedbed was proposed. A straw gather-mulch device matching with combined precision rapeseed seeder was designed. Through theoretical analysis, the structural parameters, installation position and angle, and working speed range of the key components of the straw mulching device were determined. Carrying the performance tests, controlling the straw feed rate of 0.9kg/s, 1.1kg/s and 1.3kg/s respectively, the feasibility of the working speed of each component was determined by theoretical analysis and the stability of straw transportation were verified. The experiment showed when the seeding straw mulching operation unit was equipped with a tractor of 69.9kW, at the operation speed of 0.7m/s, the roller speed of the pickup device was 80r/min, the speed of auger and chain lifting device of straw collecting device was 270r/min, the planter and components worked steadily, and the straw picking rate could reach 90%. Controlling the speed of the uniform placement device to be 210r/min, 240r/min, 270r/min, 300r/min and 330r/min, the experiment showed when the rotational speed was 300r/min, the uniformity rate of straw covering was over 92%. The field experiment showed that the straw had gathered clearly and mulched appropriately, the working parts of each link were stable, and the design indexes all met the technical requirements. The research showed that the designed straw gather-mulch device was integrated with the combined precision rapeseed seeder, which could complete the rice straw picking, stacking, transporting, rotating tillage, furrow opening, fertilizing, rapeseed seeding and mulching of rice straw in one operation, and it was suitable for the operation of rice stubble field without any treatment of straw after harvest.