Users not only focus on functional performance requirements in equipment development, but also emphasize the importance of reliability requirements. It is crucial to adopt scientific and reasonable indicators to measure the level of product reliability, guide design improvements, and support test verification. Currently, the comprehensive trade-off method is commonly used to determine reliability indices. However, there are issues with the unclear mapping relationship between reliability use requirements and the characterization of reliability indices in this process. The main problems include the transformation from abstract reliability indices to manufacturability indices and the multi-level decomposition of reliability indices for the system, components, and units. These shortcomings result in the abstraction of the reliability index concept, unclear responsibilities between users and researchers, and poor correlation of indices at each system level. Axiomatic design, which aims to systematically and clearly express the solving process from high-level abstract design concepts to low-level detailed specifics, addresses these challenges. Therefore, this paper introduces the theory of axiomatic design and constructs a product reliability index identification model based on axiomatic design principles. The model facilitates the transfer process from task requirements to reliability indices through domain mapping, enhancing the rationality and comprehensiveness of index types. Furthermore, the study uses a gas turbine as an example to determine its reliability index types. The findings of this research are expected to provide a useful reference for the systematic and clear development of the gas turbine reliability index identification process.