In this paper, the data dependencies and lossless join decomposition in dense linear order constraint databases are studied. Several concepts of the dense linear order constraint databases are introduced. The concept of the multi-region existence dependencies is defined and studied. It is proved that the lossless join decomposition of constraint relational scheme preserves if and only if they satisfies variable independence and multi-region existence dependencies. Another dependency——partitioned multi-region existence dependencies is given. The issue of variable set under linear transformation is also proposed.