Metastable　miscibility　gap　and　spinodal　decomposition　boundary　in　Cu-Ti　alloys　have　been　established　by　thermodynamic　calculation,　in　which　a　developed　regular　solution　model　and　limited　thermodynamic　experimental　data　have　been　used.　II　was　found　that　the　coherent　strain　energy　has　less　influence　on　spinodal　decompositionn　in　Cu-Ti　alloys,　and　chemical　spinodal　decomposition　boundary　and　coherent　one　are　roughly　overlapping.　The　calculated　results　are　in　coincidence　with　other　experimental　data.