The effectiveness evaluation of C4ISR system is an important link of the current research. Correctly and exactly evaluating the system effectiveness is an important means of decreasing cost and raising usage effectiveness of weapon equipment. In view of the complexity and changefulness of the diverse random events in deciding the competency matrix C and the fact that some criterions lack quantified representation in ADC method, an improvement on the method is proposed in this paper. Through the combination of qualitative and quantitative processes, ADC method, analytic hierarchical process and Delphi method are used jointly to implement the effectiveness evaluation of C4ISR systems. Firstly, the evaluation method employed in this paper, i.e. the improved ADC method, is determined based on the analysis of the advantages and disadvantages of the conventional ADC method. Secondly, the evaluation criteria and the primary evaluation process of C4ISR systems are established. Thirdly, availability vector A, dependability matrix D, competency matrix C and the computational models of their sub models are set up respectively. The process of establishing competency matrix C and its sub model is described emphatically, by applying the analytic hierarchy process and Delphi method synthetically, based on the ADC method. And finally the effectiveness and availability of the established model are verified through the calculation and analysis of examples.