The modular construction method is efficient for line production processes in factories. However, many modular unit production factories are having difficulty that how to prevent bottleneck effect, rework, and work congestion through the appropriate level of work packages composition by each work stations to achieve the smooth production. To solve these problems and improve production flow, the authors of this paper propose an optimized construction process at the factory production stage using a Dependency Structure Matrix (DSM) that considers the process approach based on flow of construction information in work activities. To test its effectiveness, the proposed process was applied to a modular factory and was found to reduce the number of main activities from 65 to 43 in comparison with as-is processes. Using this method, a manufacturing manager can thus improve production flow by analyzing the characteristics of work activities that form the plan for the manufacturing sequence decision phase. Moreover, while modular activities are independent of main assembly, there exist strong internal dependencies among these activities such that the manager can check the quality of each module. Furthermore, the research here might help save time in the manufacturing phase in factories.