The health evaluation(HE for short) is increasingly becoming a key factor restricting equipment availability. PHM design is an important means to achieve this ability, and PHM index demonstration is an important content of PHM design. Aiming at lack of theoretical and implementable methods, this article proposes a graded demonstration method from comprehensive efficiency indicators to PHM comprehensive indicators, and then to PHM capability indicators. Firstly, an HE rate is defined, and then availability is selected as the top-level input indicator. Starting from the classic definition of availability, the relationship between availability and HE rate is derived. By drawing availability curves and maximizing availability, the optimal HE rate is obtained. It’s also deduced that the HE rate is equal to the product of fault coverage and evaluation accuracy, which depend on the number of sensing units and diagnostic/prognostic methods, respectively. This conclusion can guide PHM design. Finally, the effectiveness and practicality of this method are verified through cases of inherent availability and operational availability.