In response to the fact that a large amount of straw and sticky soil of oilseed rape direct seeding in the middle and lower reaches of the Yangtze River, from the perspective of combining oilseed rape seedbed preparation and deep fertilizer application operation, a preparation method of seedbed with the whole width of the compartment shallowly rotated and the seeding belt rotated and cut for deep loosening and deep application of fertilizer was proposed, and a rotary-cutting combined deep fertilizer application device was designed. Based on the characteristics of rice root distribution in the previous crop in the tillage layer, combined with the root growth characteristics of rapeseed plants, the fertilizer depth of 100~150 mm and the deep loosening depth of 200 mm were determined; based on the kinetic analysis of the stubble cutting and breaking disc to cut off the stubble force, and the notch slip-cutting curves were qualitatively analyzed, the radius of the disc, the angle of the slip-cutting and the number of the notches were determined; based on the plowing depth, key parameters of the deep loosening and breaking shovels were determined; and the key parameters of the rotary-cutting and breaking shovel were determined through the single disturbed area, and the row spacing of rotary-cutting combined deep fertilizer application device was obtained. Using discrete element software to simulate the operational performance of a rotary-cutting combined deep fertilizer application device, the results showed that when the fertilizer depth was 150 mm, the seed bed belt was reasonably constructed, and the straw was evenly mixed and buried. The fertilizer depth was 156.60 mm, with a depth stability coefficient of 87.46%, and a uniformity coefficient of 13.18%. The field performance test showed that when the fertilizer depth was 150 mm, the stubble burying rate was 86.65%; the plowing depth of the seed bed belt and non-seed bed belt was 191.17 mm and 112.50 mm, respectively; the stability coefficient of plowing depth was 90.70% and 91.18%, respectively; the actual fertilizer depth was 149.44 mm, and the qualified rate of fertilizer depth was 85.80%. The field sowing test showed that when the fertilizer depth was 150 mm, the actual fertilizer depth was 151.56 mm, the qualified rate of fertilizer depth was 85.83%, the coefficient of variation of fertilizer uniformity was 14.33%, and the seedling emergence rate under the treatment of rotary-cutting combined deep fertilizer device was 88.97%, which was higher than that of rotary-tillage mixed fertilizer and rotary-tillage without fertilizer, and the length of the main root in the flowering stage was increased by 22.24% and 38.26%, the diameter of the main root neck was increased by 0.60% and 3.57%, and rapeseed yield was increased by 14.02% and 37.50%, respectively. The results showed that the rotary-cutting combined deep fertilization device provided a suitable seedbed strip and fertilization effect for the growth of oilseed rape, which could provide a reference for the preparation of seedbed and deep fertilization for mechanized direct seeding of oilseed rape.