The invention provides a fault detection early warming device for a steering lamp of a motor truck, belonging to the technical field of the safety performance detection of a highway transport vehicle. A vehicle-mounted terminal of the device obtains output voltage signals of a bracing wire type potentiometer, a calibration resistor and a photoconductive resistor respectively; the output voltage change of the bracing wire type potentiometer is used for detecting the steering driving behavior of a driver; the output voltage of the calibration resistor is used for judging whether a power supply circuit of a steering system can normally work or not, and a photoisolator is used for isolating the calibration resistor from a power supply loop of the steering system, so that the output voltage measuring result of the calibration resistor is more stable and accurate; and the photoconductive resistor-based photoelectric characteristic is used for detecting the working condition of the steering lamp. The device can be used for automatically detecting the fault of the steering system in real time, is convenient for the motor truck driver to maintain the fault of the steering system during long-distance transporting process, and can prevent traffic accidents. The device is simple in structure, low in cost, easy to connect with a primary circuit of an automobile, and convenient to popularize and use; and a single chip microcomputer is taken as a vehicle-mounted terminal, so that the device is convenient for the function extension of a follow-up system platform.