Abstract: To investigate the disturbance rejection capacity of decentralized control systems, a new assessing standard isproposed by introducing full relative disturbance gain matrix with investigation of disturbance gain under every state andconsidering the situations when control loops are in different operation modes. The standard overcomes the shortcomings ofexisting methods, and is an overall evaluation measure for the whole control system. The studies on a numerical exampleand a gasifier benchmark problem show that the proposed standard is a useful tool for designing the decentralized controlstructure.