In order to group web pages, vector space models for analyzing documents similarities have been often used variously. However, they are not used for analyzing link structures, partly because they are complex and links do not necessarily satisfy the similarity relation. If we can devise vector space models for link structures, we can combine them with those models for document similarity in order to develop the unified basis for grouping Web pages. In this paper, we present a vector space model for link structures, based on the notion of link vectors, the specifically designed characteristic vectors for link structures. We also discuss the extension of this model to the model called content-link vector space model, which can treat document information and link information of Web pages in a unified way. The preliminary experiments show that the models show good performance even when document information is ignored.