A set of automatic excavation depth control system was designed by comprehensively using sensor technology， hydraulic control technology and PLC control technology to solve the problems of unstable excavation depth of the 4UML-130 vibrating chain cassava harvester， which results in large damage of cassava and high energy consumption. The system designed was made up of profiling mechanism， excavation depth detection mechanism， hydraulic system and control system. The integral separation fuzzy PID algorithm was used to adjust the excavation depth in real time， which effectively achieves the accurate control of excavation depth. The results of simulation and indoor test showed that the overshoot of the control system using integral separation fuzzy PID algorithm was the smallest and the time to reach stability was the shortest in the step response experiment. The error of the control system using integral separation fuzzy PID algorithm in the sinusoidal response experiment was ±0.5 cm， significantly better than that of the other methods.