Field experience indicates that hydrates formed in pipelines/wellbore may result in severe conduit blockage and Other safety problems in oil/gas development. For gas-dominated systems, one key step to address the,hydrate problems is the coupling of multiphase flow and hydrate behavior (formation, deposition, etc.), which has not been well studied so far. hi, this paper, a hydro-thermo-hydrate coupling model or a gas-dominated system is developed by considering the interactions between multiphase flow and hydrate occurrence which is described as layer growth from hydrate deposition on the wall. The accuracy and reliability of the proposed model have been verified with field and literature data. By using the new model, hydrate formation and deposition during deepwater gas well testing operations are simulated, For a typical deepwater gas well (water depth 1500 m, gas production rate similar to 50 x 10(4) m(3)/d, liquid holdup similar to 3%, without inhibitors), it takes 30 or more hours for hydrates to block the testing tubing. The hydrate blockage can-be significantly promoted by the presence of a free water phase and postponed by the injection of inhibitors. The proposed model makes it possible-to predict when and where hydrate blockage will occur in the tubing during a deepwater gas well testing. This work adds further-insights into characterizing the interactions of the complicated systems and provides guidance for hydrate management Optimization.