In group decision making problems, decision matrix depends on different attributes. The weight of each attribute indicates its relative importance comparing to others. The objective of this paper, however, is to introduce a linear model in order to determine the importance of each attribute in multi attribute group decision making problems with intuitionistic fuzzy data; so that, this model prevents the decision makers from making mistake in determining the weight and shape of standardization of their mental measurement units. Next, using the determined weights, a new method of ranking alternatives based on ELECTRE III is introduced and illustrated. In this method, group satisfaction index is used to exclude decision makers' personal opinion for selection the best alternative. Finally, a numerical example is considered to elucidate the details of the proposed method, and then the obtained results are compared with other current methods.