Abstract: As one kind of typical network big data, social-information networks such as Weibo and Twitter include both the complex network structure among users and rich microblog/Tweet information published by users. It is notable that most of the existing methods only make use of the network topological information or the non-topological information for link prediction, but there is still a lack of effective methods by fusing the topological information or non-topological information in social-information networks. A link prediction method is proposed from the perspective of users’ topic by fusing users’ topic similarity in social-information networks. The method goes in accordance with the following sequence: firstly, a topic similarity between users based on users’ topic representation is defined, followed by which a topic similarity-based sparse network is constructed; secondly, the information of the following/followed network and the topic similarity-based network are fused into a unified framework of probabilistic matrix factorization, based on which the latent-feature representation of the network nodes and the linking relation parameters are obtained; finally, the linking probability between network nodes is calculated based on the obtained latent-feature representation and linking relation parameters. The proposed approach provides a general modeling strategy fusing multi-network information and a learning-based solution. Link prediction experiments are conducted on four real network datasets, i.e. Twitter and Weibo. The experimental results demonstrate that the proposed method is more effective than others.