Even though the final source selection of foreign weapon system purchase project in defense area is the most important phase, the standard evaluation index has not been developed. This paper provides an appropriate evaluation index using DEMATEL and ANP methods. First, the all possible evaluation criteria applied to the relevant previous literatures in domestic and overseas researches are derived and classified into groups. Second, DEMATEL method is used to determine the network structure representing the relations of cause and effect between groups and their sub-criteria. If isolated factors, not connected with other factors, are existed in the network structure, all factors except for the isolated ones are grouped as one large factor so that the independency between those ones is maintained. The weights of criteria are determined using AHP method if the criteria are independent relation and ANP method if the criteria are networked. The weights of higher and lower level criteria are then integrated and distributed as a point with respect to the decision making purpose. The developed evaluation index can be used as a standard one in various foreign weapon system purchase projects in defense area.