Diverse stakeholders engaging in design, construction, and operation and maintenance of offshore plant typically operate heterogeneous plant 3D CAD systems. Engineering, procurement and construction (EPC) companies should deliver plant design result to an owner in the form of plant 3D CAD model specified in the contract. However, due to the limitation of data interface of plant 3D CAD systems, EPC companies frequently perform manual remodeling to fulfill the terms and conditions of contract. Therefore comparison should be performed between source plant 3D CAD model and remodeled plant 3D CAD model in order to prove the validity of remodeled plant 3D CAD model. In order to automate the comparison process, we developed a system for quantitatively assessing the similarity of plant 3D CAD models. In addition, experiment results using the comparison system are explained.