In the earlier stage of architectural design process, the decision making on design alternatives comes to be the key factor. Thus, in order to apply BIM from the earlier stage of design, software to support decision making becomes the essential part. This study aims to develop software to support the earlier stage decision making in design process, which works by analyzing and evaluating the layout structure of design alternatives. The spatial analysis software developed through this study is based on the network-based spatial analysis technique, and fully interworks with existing BIM software. In the latter part of this paper, the newly developed software was applied to the BIM model of an actual architectural space for analysis and evaluation, through which process the validity was proved that it could be justifiably applied to the earlier stage of BIM design process.