A set of automatic control system of sugarcane harvester cutter was designed to solve the problem that the sugarcane harvester cutter cannot automatically control the depth of cutting device， which affects the quality of harvest. The system mainly included angle profile mechanism， depth detection system， hydraulic system and control system. The fuzzy PID control algorithm optimized by genetic algorithm was used to adjust the depth of the soil in real time through Simulink step response and step response with random interference simulation. The results showed that the overshoot of fuzzy PID control algorithm optimized by genetic algorithm was 4.9%. The adjustment time was 1.535 s， being improved compared with PID control algorithm and fuzzy PID control algorithm. The results of comparing laboratory test showed that the error of fuzzy PID control algorithm optimized by genetic algorithm was （-0.5，0.5）， which was the smallest， indicating that it automatically control the depth of the cutter effectively.