Authors already reported the integrated system so called SODAS (System Of Design and Assembling for Shipbuilding) which was based on product model concept. And products in shipbuilding industry today are not limited to ship structures alone. Therefore, it is desirable that a more global product model which can describe another products such as offshore structures should be considered. In this paper, a product model of offshore structures is discussed. Compared with the case of ship structures, the distinctive feature in the design stage of offshore structures lies in the initial design stage. Thus in this paper, some of the new model in initial design stage are introduced. Some of them are “Function Element Model” which expresses functional concept by designers. In the other design stage, product information such as “Room” and “Part” which were already introduced in SODAS are used effectively for a product model of offshore structures. By the use of product information such as “Function Element Model”, “Room”, “Part”, and so on, many kinds of information are described in the system. As the result, a product model of offshore structures is implemented in SODAS. Some examples using this system are shown at the end of this paper.