The article is an attempt to create ontology of test and diagnostics systems for blading power plants. Ontology is considered as a formal construction that combines understanding of the object model (more adequately -the subject area) from a logical point of view (as interpretation of a formal system that satisfies the axioms), from an algebraic point of view (as a set of objects belonging to certain classes with certain relations), in general scientific terms (as a simplified representation of objects, phenomena and processes of the real world). The prospective use of the model is associated with support for the development of test and diagnostics systems for blading power plants. The support is interpreted as a process of meeting the technical requirements, certain methods implemented by certain means.