Abstract: Flotation perfect index as a key indicator in evaluation of flotation performance plays a vital role in making rational guidance of flotation operations. However, in recent years, its applicability has become a controversial issue among different schools in coal industry. For better elucidation of the contentious points, following an elaboration on the definition, scope of application and physical meaning of the flotation perfect index, an analysis is made of the applicability of the index in evaluation of performance of flotation operations under different operating scenarios in coal preparation plant. As indicated by analysis result, the index can reflect to a certain extent the degree of misplacement of combustible matters and ash-forming minerals in separated products; its scope of application is difficult to be clearly defined; the physical meaning of the index does not tally with the aim to be attained by flotation; and there exists poor comparability of data obtained. It is therefore inadvisable to evaluate performance of flotation operations in coal preparation plant with the flotation perfect index as a core indicator alone.