Abstract: A state sensor for air door is designed based on ultrasonic technology and magnetically sensitive components. The air door structure of the main fan in the coal mine is introduced. The overall architecture of the state sensor for air door and the principle of the main devices are analyzed in detail. The ARM embedded chip is used as the core, the opening of the air door is detected by ultrasonic components with temperature compensation technology, and the limit position of the air door is detected by using magnetically sensitive components, thus the solution of air door state monitoring is built. The actual installation location on site is analyzed, and the change of operating condition parameters in the process of air door action is studied.