Abstract: A similarity degree of vague value was firstly proposed, then a new weighted similarity measure of vague sets was given based on OWA operator, in which the weights were produced according to the requirement of decision maker.Finally, a simple bidirectional vague reasoning method for vague decision system was put forward on the basis of similarity measure between vague fact and the antecedent (or consequent)portion of vague rule. The presented method is very flexible and feasible, which provides a powerful tool for dealing with vague decision making problems in complex enviroment such as industry inspection and medical diagnosis systems.

Key words: Vague set, Weighted similarity measure, OWA operator,Bidirectional approximate reasoning, Vague decision