Abstract: The depth control system of the agricultural machinery includes three aspects, depth measurement, driving actuator and control algorithm.The measurement accuracy of contact and non-contact depth measurement technology can reach the mm-level, but the advantage of non-contact measurement technology is larger in the measurement device integration and the response speed, which is the future development direction.The working speed of agricultural machinery is not high, and the bearing capacity is large, so the depth control system is mainly driven by hydraulic actuator, which is little room for change.PID control algorithm is the most widely used in depth control of agricultural machinery, its control precision can reach cm-level, and a small part can reach mm-level.However, PID control algorithm has insufficient capability in overcoming external strong disturbance and load change, thus more advanced control algorithms will be applied in this field.