Considering the soil in Midlower Yangtze River is sticky and its moisture content fluctuates greatly, the furrow should be ditched while rapeseed planting. Due to the lack of theoretical basis for the design of resistance reduction of plow surface, the research on soil contract surface optimization of ship type ditching system was carried out by using the method of differential geometry analysis and EDEM simulation. According to the traction resistance analysis and surface parameter analysis of the main contact surface (front plow surface, shaping surface), the main structural parameters range of the contact surface was determined. Based on the theory of differential geometry, the differential geometric expression which can quantitatively describe the spatial shape change of plow surface with straight, parabolic and exponential curves was established. The simulation results of traction resistance characteristics indicated that the parabolic type plows had better resistance reduction characteristics when the operating velocity was 0.9~1.5m/s. And its resistance were reduced by 15.09%, 16.92% and 32.59%, 31.58% respectively compared with the linear type plows and exponential type plows. The intrinsic geometric parameters E, L and M can respectively reflect the growth rate of traction resistance with speed, the magnitude of traction resistance, and the fluctuation degree of traction resistance with speed. The parameter optimization results indicated that when the operating velocity was 1.2m/s, the width of ditching plow w was 92mm and maximum element angle Φmax was 66°, the minimum traction resistance was 104252N. Field experiment indicated that the average traction resistance of the combined shiptype ditching system optimized by parameters were 956.77N, 1101.33N and 1 564.85N, and the error between the system and the simulation test results was less than 7%, and the operation effect met the agronomic requirements of rapeseed planting. The research conclusion had great theoretical value and practical significance to the resistance reduction design of plow which formed by horizontal straight line principle.