The false alarm of the BIT based on model in the mechatronics control system is studied. Firstly, the information uncertainty of the BIT system and the reason of BIT false alarm are analyzed. Then, the BIT system is designed by the application of the optimal UIO(unknown input observer). It is robust to the information uncertainty, and can decrease the false alarm. Finally, the experimentation on the BIT system of stabilization and automatic pointing and tracking platform is made. The result shows that the analysis is correct and the method is effective.