Abstract: Abstract: In the rice-wheat crop rotation and other type of double cropping system areas, a large number of straws were left in filed after harvesting. Most areas need the twice field preparation for crop production so that straw could be returned to soil. In order to solve the problems of straw-returning and soil preparation in the rice-wheat crop rotation, the plowing and rotary tilling compound soil preparation machine was designed. The compound soil preparation machine mainly included plough mechanism, rotary tilling mechanism and rack. There were four plough bodies installed in the plough frame of the compound soil preparation machine and two rotary tilling knife rolls divided by the auxiliary gear box installed in the rotary tilling frame of the machine. There were 26 couple rotary tilling blades installed in the left and right knife roll and ranging by double helical line. The interaction of the plowing mechanism and the rotary tilling mechanism when the compound soil preparation machine was working was mainly considered in the designing process. For balancing couples of ploughing, the rotary tilling frame was offset 210 mm to right. For making the soil was shatter better, the distances that two rotary blades of close to the auxiliary gear box on the left and right knife roll to the auxiliary gear box were 50 mm. The compound soil preparation machine was studied in this paper based on the theory of discrete element method (DEM). The dynamical model of the compound soil preparation machine was established based on its working principle. The DEM model of the compound soil preparation machine was established by the discrete element software EDEM and the virtual simulation of working situation was carried out. The simulation results showed that the broken rate of soil of the compound soil preparation machine was 91.4% and the surface roughness of the machine was less than 2 cm. A field experiment was conducted to validate the rationality of designing methods and working performance of the compound soil preparation machine. The results of field experiment showed that working condition tillage deep and working condition tillage wide were 21.6 cm and 1.98 m, and working condition tillage deep stability and working condition tillage wide stability were 91.3% and 96.7%. The results showed that working situation of the compound soil preparation machine was stable. The surface roughness of the compound soil preparation machine was 1.87 cm and the broken rate of soil and vegetation coverage of the machine all were greater than 90%. The results showed that quality of soil preparation met requirement of agriculture production in the rice-wheat double cropping system area. The fuel consumption and productivity were 15.9 kg/hm2 and 0.38 hm2/h. The control group that plough machine and rotary tilling machine were secondary tillage operations was set up. The results of control group experiment showed that the various experimental results of the compound soil preparation machine were better than the results of control group. Especially in fuel consumption and productivity index, the compound soil preparation machine was far better than the control group. The control experiment explained that the compound soil preparation machine was energy conservation and efficient to the traditional cultivation method.