By reviewing the published works and papers concerning the three-clans-allied marriage, the author shows that it is important to clarify some issues. Based on a case study of the current situation of the three-clans-allied marriage among the Bru-Van Kieu in Ta Rung Village (Huc Commune, Huong Hoa District, Quang Tri Province), the author states that it is crucial to add a "self-contained" factor in the above-mentioned marriage to create a "line, one-dimensional, and self-contained" marital rule as in reality. His finding is partly different from previous studies that show a line and one-dimensional model of the Bru-Van Kieu's marriage. A deep cause of the appearance, existence and destruction of the three-clans-allied marriage is economic. In addition, a situation that a family is simultaneously a member of marital multi-alliance contributes to maintaining such the marriage.