Health monitoring technology is the key technology to improve the safety, combat readiness and quick response ability of equipment, which has become the necessary technology of modern high-tech equipment. In order to characterize the aircraft health status clearly and effectively, the parameters "health degree was put forward to characterize the health level of aircraft and its sub-systems, which refers to the extent that the aircraft and its sub-systems keep sound and their functions are not weakened when the aircraft and its sub-systems are completing the specified tasks under the specified conditions. Here the health degree has two expressions, which are the basic health degree and the mission health degree. Based on it, the calculation and determination methods of the basic health degree and the mission health degree of aircraft and its sub-systems were given out. Then, the health status evaluation methods of aircraft and its sub-systems were established based on the "health degree as well as the “healthy”, “sub-healthy” and “unhealthy” employed to express the typical three healthy statuses of them. Finally, the condition-based maintenance (CBM) strategies for aircraft and its sub-systems based on the health statuses were described by means of an example: the aircraft and its sub-systems don’t need maintenance when they are healthy, the aircraft and its sub-systems need to make maintenance plan when they are sub-healthy, the aircraft and its sub-systems need maintenance at once when they are unhealthy, and the final implementation maintenance strategy should be carried out considering the economic requirements. The results of this paper lay a foundation for the effective applications of health monitoring technology in aircraft and its sub-systems, and they can also be extended to the health monitoring of other equipment and systems.