In recent times, there is a growing demand for technologies that control the level of detail (LOD) of large-scale three-dimensional (3D) computer-aided design (CAD) models. In particular, in industrial plants and in the construction industry, there is a significant need for simplification of large-scale models, because the number of models to be dealt with is tremendously large and their complexity is high. The degree of automation is, however, very low in these industries. As a result, many additional costs arise in the process of manually regenerating the 3D CAD models by the users. To resolve this problem, this study suggests a way to control effectively the LOD of large-scale B-rep assembly models. The proposed method consists of filtering, to remove those parts that ought to be removed, and progressive control, to remove sequentially the features acquired by volume decomposition. The user intervenes in the progressive control stage and adjusts the LOD for each component of the assembly. Based on the proposed method, a prototype system was implemented and experiments were performed for two test cases. The data size of the two test cases decreased, in average, to 65% in the first stage and 85% in the second stage. It was also found that the proposed component-level LOD control method is suitable and practical for a large-scale model.