The invention relates to an automatic fault diagnosis system of a bulldozer. A controller and a display are connected with a CAN wire. The controller comprises an engine controller, a detection controller and a traveling controller. Each engine parameter sensor is connected with the engine controller; a bulldozer transmission and working parameter sensor, a bulldozer starting system electrical device detection points are connected with the detection controller; and a travelling control handle, a travelling brake pedal, a travelling solenoid valve, a steering brake solenoid valve and a bulldozer travelling pressure and velocity sensor are connected with the traveling controller. The invention can diagnose all faults of the electrical devices, lines, and part of hydraulic system of bulldozer, alarm and display the detected content, thus an operator can find the fault points directly according to indication of alarm, and then eliminate the faults effectively. Therefore, labor intensity is reduced and downtime is shortened, and the maintenance cost is reduced. The automatic fault diagnosis system can make sure the bulldozer operate safely and improve the overall management level of the bulldozer. The invention has the advantages of stable performance, convenient operation, safety and reliability and humanized interface.