Abstract: An agile design and integration method for loitering unit products based on the Modular Open Systems Approach (MOSA) and the integration of civil and commercial industrial chains is proposed. The U.S. military’s Modular Open Systems Approach (MOSA) is studied in depth, and in combination with the Model-Based Systems Engineering (MBSE) methodology and relevant tools, the design process of the loitering unit system architecture is systematically sorted out. Relying on the civil and commercial industrial chains, the rapid design and integration of the system scheme are accomplished. An openness evaluation index system for the loitering unit system architecture based on the integration of civil and commercial industrial chains is established, which provides guidance for the optimization of the architecture. The results show that this method can greatly shorten the development cycle of the loitering unit system, reduce the development costs, and promote the agile upgrading of system capabilities.