Aiming at the problems of heavy and wet soil in agricultural areas in the middle and lower reaches of the Yangtze River, poor surface flatness due to machine rolling, and unstable tillage depth during farming. Firstly, the posture of the rotary tillage operation unit was analyzed, the geometric relationship between tillage depth and angle was determined, and the tillage depth control model was established. The angle displacement sensor and the tilt angle sensor were used to measure the rotation angle of the lift arm and the pitch angle of the tractor body to indirectly determine the tillage depth. Secondly, an electro-hydraulic monitoring system was designed, which can realize preset tillage depth value and display real-time tillage depth. Finally, Simulink software simulation was used to test the response speed of the tillage electro-hydraulic monitoring system. The simulation results showed that the system can reach a stable state in 0.6s and meet the tillage depth control requirements. In the field test stage, the accuracy test of the automatic tillage depth detection system was adopted, and the test result was obtained that the system which can detect the change in the height value of the three-point suspension drop-bar suspension point caused by the tilt, and the control height was stable at the set value. The performance of the automatic detection system for tillage depth was verified. In order to test the field operation performance of tillage depth electro-hydraulic monitoring device, the designed electro-hydraulic monitoring system and the original mechanical control system were selected for comparison tests. The results showed that when the electro-hydraulic monitoring system was used for rotary tillage operations, the value of the variation coefficient of tillage depth stability was 4.28% under each working condition at most. The standard deviation of tillage depth and the coefficient of variation of tillage depth stability were both lower than that of the mechanical control system. It was verified that the electro-hydraulic monitoring system improved the stability of tillage depth and can achieve a good stable tillage effect.