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At present, some problems of rice straw returning machine still exist in China, such as shallow tillage depth, straw countersfield depth can not meet the agronomic requirements, and rotary parts are easy to winding straw, etc. A new kind of rice straw deep buried and whole straw returning device was designed by using the rotary tillage theory and numerical calculation analysis. With the hypothesis of soil particles based on the actual situation, the mechanical model of soil particles was established and the simulated virtual experiment of whole straw returning device was carried out by applying the discrete element method (EDEM). As a result, the coverage rate of topsoil reached 93.87% when the tilling depth was 20cm. By the soilbin bench tests, the following results were obtained: when the operation speed was 1.25km/h and the speed of knife roller was 237r/min, the tillage depth could reach 22cm; straws buried below the surface in 15~20cm accounted for about 80% of the total straw; the topsoil coverage rate was 91.63%; and the knife roller shaft would not wrap the straws. The test results showed that straw buried depth can meet the requirements of paddy field tillage link and the topsoil coverage rate was high. Through the mutual verification between virtual simulation and bench test, it is proved that the design of whole straw returning device could realize the functions of cutting soil, breaking soil, burying grass, pressing grass and covering soil, which meets the agricultural requirements well.