According to the detection process of vehicle headlight adjuster, and the automation testing requirements proposed by the factory, an automatic test system is designed based on microcontroller (MCU) STM32F103. Using Alternating Current (AC) servo motor loading mode, the workload of the headlight adjuster was accurately simulated through closed-loop control and Proportion Integral Derivative (PID) feedback adjustment.The dynamic signals such as working current, maximum current, load resistance and motor displacement were collected in real time at each control voltage stage.The performance of the headlight adjuster was judged by comparing the parameters in the detection scheme, and displaying real-time curves and judging results in man-machine interface(MMI). Compared with the traditional single piece manual inspection, the automatic detection device has the advantages of high efficiency, high accuracy, and automatic data collection and analysis.