Public online social network services have achieved dazzling success in recent years. As a result, vertical social network services for universities are expected warmly by campus users. As the majority of activities in university campus are knowledge and social interaction intensive, one of the core functions of campus social network system is to facilitate knowledge sharing on campus. In the cyberspace of universities, knowledge is stored in various kinds of digital resources such as documents, photos, videos etc. In this paper, we discuss the design and implementation of our campus social network system, concentrating on knowledge sharing mechanism in the system. The knowledge sharing mechanism has five features including the utilization of users’ personal social network to facilitate the dissemination of digital resources, the use of a six-tuple model based tagging to realize the unified labeling for digital resources, the fine-grained access control based on friend lists for safer knowledge sharing, the adoption of a multiscale evaluation method for digital resources and personalized recommendation for digital resource with social graph based collaborative filtering as its core idea. With all these considerations, we expect to improve the efficiency and effectiveness of knowledge while enlarging the dissemination scope of digital resources carrying it in cyberspace of universities.