Abstract: Abstract: In order to reduce tillage resistance, ameliorate the soil layer structure and improve soil breaking rate of soil crushing roller, a combined tillage machine which has function of subsoiling, rotary tillage and soil breaking was designed in this paper. The machine mainly consists of a fixed mount to connect the subsoiler, rotary and soil crushing roller with the machine frame, the self-excited vibration subsoiler breaks the bottom of the plow pan, the rotary tiller flattens the soil and further shreds the soil, the soil crushing roller further breaks the soil thus creating a seedbed suitable for plant growth. 2 major components of machine are optimized to solve the problem of large tillage resistance and poor soil breaking effect. Firstly, the self-excited vibration subsoiler with controllable penetration angle was designed, which can avoid the problem of poor drag reduction effect and stability of tillage depth when the penetration angle of subsoiler is too large. The subsoiler produces a vibration to loosen the soil to achieve the purpose of drag reduction because of resistance changes in soil operation. In addition, the penetration angle of subsoiler is controlled to a range to maintain the stability of subsoiling depth. To ensure the compression spring can not be tilted during the subsoiling operation, and considering the problem of large load and limited installation space, the combination spring is selected as the self-excited vibration spring. Through the kinematics and mechanical model of self-excited vibration subsoiler, the deflection is 15 mm and the minimum and maximum loads are 7 500 and 15 000 N respectively, then the parameters of the combined spring was determined. Secondly, in order to realize the secondary soil-broken function, a caged soil crushing roller was designed by staggered welding of rhombic soil-broken teeth on a cylindrical drum with clearance. The soil is first broken by the outside teeth of soil-broken tooth, and the large soil will enter the cylindrical drum inside through the gap and will broken under the action of inside teeth, which can't adhere to the cylindrical drum. The caged soil crushing roller diameter and thickness of soil-broken teeth is calculated according to the design formula of the disc harrow. To study the drag reduction effect and tillage quality of self-excited vibration subsoiler, the experiment in the soil bin is carried out, and the field experiment of operation performance of the machine is carried out. The soil bin experiment results showed that the self-excited vibration subsoiler has obvious effect on drag reduction, and the average drag reduction is 9.22%, and the soil fluffy degree and disturbance coefficient is 26.16% and 77.21% respectively. The field experiment results showed that the stability coefficient of subsoiling depth, stability coefficient of depth of soil preparation, surface flatness, vegetation coverage and soil breaking rate is 94.92%, 92.50%, 1.17cm, 93.36% and 84.18% respectively. The soil breaking rate of ordinary soil crushing roller is 71.41%, which indicates that the caged soil crushing roller can effectively improve the soil breaking effect. Moreover, the caged soil crushing roller did not appear soil adhesion and congestion during the test. All parameters meet the requirements of the work quality standards. Therefore, the machine has obvious effect of reducing resistance and quality of the soil preparation. This study can provide a theoretical reference for further research of combined tillage machine of subsoiling and rotary.