Ternary phase diagram for CVD diamond has been calculated in the ternary system C-H-halogen at various temperature and pressure to identify the diamond growth region. There are diamond growth regions in these phase diagrams. it reveals that the possible mixture composition for diamond growth is confined in diamond growth region. Diamond growth region changes greatly with temperature in halogen addition systems. There is a similar trend of diamond growth region at high temperature in the systems of C-H-chlorine, C-H-brornine and C-H-iodine. The different feature is that diamond growth region exist in halogen-rich region in C-H-chlorine system, for which very little experimental data is reported. The comparison with experimental data suggests that the calculated phase diagrams can be predictable for optimizing growth conditions of CVD diamond.