Abstract: Persistent drought can often occur during the rapeseed sowing period in the mid-lower reaches of the Yangtze River. Traditional rotary tillage devices cannot fully meet the large-scale production in recent years, due mainly to the excessive stubble residue after rice harvesting, less straw returning, and low seedling emergence rates. In this study, the rapeseed direct seeding machine was developed with stubble covering using a combined harvester platform. The harvesting, tillage and seeding were integrated into the one. A single operation realized the various tasks, such as collecting, shredding, and covering stubble residue for returning to the field, as well as seedbed preparation and rapeseed sowing. The movement principle of the crank-slider mechanism was combined to improve the passability of the machine tool during field operation and transshipment, according to the structural properties of the guide rail vertical suspension device. The structure of the suspension device was also improved by kinematics analysis. There was an effective increase in the ground clearance of the rear suspension tilling and sowing system. As such, the lifting height increased by more than 50%, compared with the suspension device. In addition, the structural parameters of the threshing device were considered to achieve the straw mulching and return to the field. A straw-crushing and side-throwing device was added at the side end of the combine harvester. Furthermore, the rotational speed of the threshing cylinder was the main influencing factor on the qualified rate of straw crushing and the uniformity of straw laying. Dynamics and kinematics analysis was then conducted in the process of straw crushing and throwing. The single- and two-factor three-level central composite experiments were carried out to explore the impact of each test factor on the evaluation indexes, in order to evaluate the working performance of the whole machine. The forward speed of the machine and the engine power output speed were taken as the experimental factors. The experiment indexes were selected as the soil fragmentation rate, flatness of seedbed surface, straw shredding qualification rate, and uniformity of straw spreading. The quality of the seedbed was also evaluated under straw treatments. The response surface model was established to obtain the optimal combination of operational parameters. The experimental results showed that the forward speed and engine power output speed shared significant effects on the soil fragmentation rate, flatness of seedbed surface, straw shredding qualification rate, and uniformity of straw spreading. Once the forward speed was 2.89 km/h and the engine power output speed was 2 210 r/min, the superior performance of the machine was achieved, where the soil fragmentation rate was 85.65%, the flatness of seedbed surface was 20.06 mm, the straw shredding qualification rate was 90.31%, and the uniformity of straw spreading was 89.33%. The verification experiment was carried out using optimized round parameters, i.e., the forward speed was 3 km/h, and the engine power output speed was 2 200 r/min. The overall performance of the machine fully met the requirements, the soil fragmentation rate of 85.69%, flatness of seedbed surface of 21.32 mm, straw shredding qualification rate of 89.35%, and uniformity of straw spreading of 88.07%, with deviations from the optimal of 0.04 percentage pionts, 1.26 mm, 0.96 and 1.26 percentage points, respectively. The finding can provide technical support to the mechanized rapeseed sowing in multifunctional machinery.