An improved Grey Target (GT) approach using the Evidential Reasoning (ER) algorithm, named as ER-GT, is proposed to handle the challenge when conducting the contribution analysis in the Weapon System of Systems (WSoS) context. The WSoS technology contribution analysis is a small-sample, less-data problem without a recognized pattern, which fits the characteristics of the problems that GT is designed to solve. However, the standard system in GT may not exist at all since its indices are derived from different systems and fails to be consistent with the System Military Value (SMV), which represents the contribution made of a system to WSoS. In order to make certain adjustments of the standard system, the information derived from capabilities requirements, practical restraints and/or experts’ knowledge must be taken into consideration. Since the ER algorithm has a privilege in dealing with different types of information under uncertainty, it is applied to transform the standard system into a “mission system” so as to integrate different types of information. A comparative case using both GT and ER-GT is studied to validate the efficiency of the proposed ER-GT approach. The study result shows that the defense capability is given a bigger contribution rate, which has been neglected by traditional GT.