This paper has carried out research on task-oriented capability analysis, function analysis based on fault degradation and parameterized health assessment for complex systems represented by military aircraft. First, we obtained "aircraft based on mission analysis". Indicator) - task function (secondary indicator) - influence parameter" two-level mapping, as the object of health assessment; then, the combination of deterioration degree and severity is proposed to evaluate the "task function" secondary index, using the pole The large entropy improved interval analytic method obtains the “function” weight, introduces the penalty factor for the key functions, and evaluates the “aircraft” to obtain the whole machine health assessment result. This method starts from the actual demand and use process of military health management, and carries out method research, combined with specific example objects and parameter analysis, so the evaluation method and results are highly credible, can support task and maintenance decision, and have good engineering practical value. The application research of a certain type of aircraft is carried out, and the results prove the feasibility and practicability of the method.