In order to build an effective operation system under conditions of information, this paper describes concept of army organization formally from two aspects of organizational entity and organizational structure, and proposes a systematic adaptive design method of army organization. The idea of the proposed method is to resolve such complex problems into four relatively simple sub-problems first, i.e. operation plan design problem, operation plan adjustment problem, command and control (C2) structure design problem and C2 structure adjustment problem, and then to solve these sub-problems for the achievement of construction and dynamic evolution of army organization. The coupled relations among sub-methods used to solve the sub-problems are analyzed in detail and the input/output information of the sub-methods is ruled. On the basis of this, the design method and adjustment method of operation plan are introduced with the comprehensive consideration of task completion time and task completion quality of army organization while the design method and adjustment method of C2 structure are presented with the measurement of load level and load balancing extent of army organization. Finally, the future development of the proposed adaptive design method is given.