Abstract: BIT (Built-in Test) technology is an effective measure to improve the testability and maintainability of the airborne computers for the Characteristics that it does not rely on external equipment and uses its own software and hardware to complete fault diagnosis and isolation. "Fault coverage" and "false alarm rate" are two important factors in evaluating BIT systems. Lower fault coverage is an important reason to hinder the widespread use of BIT technology in airborne computers. Based on the analysis of the BIT fault detection mechanism in the airborne computer, a new BIT fault detection method in the airborne computer is proposed, and the key technical solutions are given in this paper. It is proved by practice that the Fault coverage has increased significantly of the airborne computer BIT systems, the reliability and maintainability of the airborne computer have increased significantly after using this strategy.