The nodes in the knowledge social networks are persons, the ties are the knowledge communications. Persons as nodes have two way knowledge flow: inflow and outflow of knowledge. There are mental processes involved during the inflow and outflow of the knowledge. Knowledge communication methods are various during the knowledge conversion processes, they can be described by four features: expressive form, intermediary form, real-time/non-real-time,one-way/interactive. The knowledge social network can be found by formal knowledge transfer organization or informal knowledge transfer relationship. Social networks also provide the motivations for learning. We give a real case of knowledge transfer in the education and career of a student and analyze the functioning mechanism of social network in the knowledge transfer process