Abstract
This paper analyzes the features of non-functional properties of Web Services, studies their classification, advance a method to dispose the uncertain features with fuzzy sets and grey systems, provide a measurement (i.e. relevance degree, based on rough sets) of dependency among the non-functional properties, which evolves a description (i.e. support degree, based on rough sets too) of essentiality how the decision factors affect the decision results, and supply a new approach of QoS evaluation.