Aiming at the problems of low efficiency of depth measurement and lack of effective online monitoring method in rotary tiller operation, a nonlinear monitoring method of rotary tillage depth based on suspended rotary tillage attitude was developed to improve the automation level of rotary tillage quality monitoring. Firstly, the suspension attitude of rotary tiller was analyzed, and the mathematical relationship between the depth and attitude of rotary tiller was established based on the geometric relationship. After comprehensively considering the influence of the structural deformation and wheel subsidence of the suspended rotary tiller group on the measurement results, a threecalibration parameter tillage depth detection model was established. The model can be used to calculate the tillage depth in real time by fitting the relationship between the attitude angle of rotary tiller and the tillage depth. Secondly, in order to verify the measurement accuracy of the model, a rotary tillage depth monitoring system suitable for vehicle terminal was designed. The system integrated satellite positioning, realtime depth measurement, operation speed measurement, operation area calculation and stability evaluation module, and realized the display of the vehicle terminal and cloud storage. Finally, the model parameters were calibrated in the field and optimized based on Matlab. The results of the calibration test showed that the tillage depth value was decreased gradually with the increase of the horizontal inclination angle of the lower link, and the two were negatively correlated, and the tillage depth value was increased gradually with the increase of the horizontal inclination angle of the frame, and the two were positively correlated. A number of field tests were conducted on the calibrated rotary tillage depth monitoring system, and the results showed that the maximum error was 0.80cm, and the rootmeansquare error was 0.55cm. When the tillage depth was about 11cm, the measured value was closer to the real value, which happened to be within the reasonable operating depth range of rotary tillage, indicating that the rotary tillage depth monitoring system had high accuracy and good stability.