In order to clarify the process of cutting heavy clay with the type IT245 rotary cultivator(knife seat type), the rotary cultivator-soil was modeled based on the smoothed particle hydrodynamics(SPH) method. Simulating by ANSYS/LS-DYNA software , the soil-cutting torque of a single rotary cutter was analyzed under the conditions of cutter head speed of 200 r/min, forward speed of 0.6 m/s, and ploughing depth of 0.12 m. The average simulated torque was 5.84 N? m. The theoretical average torque is 6.42 N?m calculated by the Ken earth pressure theory. The error between the two is 8.98%. Using the theoretical method and the finite element method respectively, the rotation-orthogonal combination test was carried out with the forward speed, the rotating speed of the cutter roller and the ploughing depth as the influencing factors, and the specific work as the evaluation index. The regression equation of the specific work of the rotary tiller was obtained dependent on the forward speed of the machine and the speed of the cutter head and the speed of the cutter head. It indicated that the larger forward speed and ploughing depth and the smaller cutter shaft speed should be selected as far as possible in the case of meeting the agronomic requirements.