With the development of Web 2.0 technologies, Web-based Social Network (WBSN) becomes a fast developing field in recent years. As there are a large number of participants on the open platforms of WBSNs, trust relation is a critical issue. In this paper, we study the features of WBSN Websites and some trust relevant models for WBSNs. We further propose a new category of "three generations of WBSNs", and analyze both theoretical studies and practical applications on trust relation establishment mechanisms in each of the first two existing generations of WBSNs. Through the analysis, we summarize the drawbacks of existing trust mechanisms and propose some trust related research issues that are expected to be solved in the future in the third generation of WBSNs.