Abstract: An important subject in control system design is to actively explore and dispose both functional and physical redundancy, which is abundant in modern control systems and of various fashion and mechanism. We first present a new concept of 'configuration redundancy', which may provide a common understanding of different kinds of redundancy. An index is then proposed based on the concept to evaluate the amount of functional and physical redundancy in a system, and consequently provides a new basis for redundancy disposition and active survivability design. The concept and index are applied to control sensor systems in detail, and some examples are provided to show the effectiveness.