Disclosed herein is a process for the preparation of dimethylether from hydrocarbons, including tri-reforming a feedstock mixture comprised of hydrocarbons, carbon dioxide and water vapor in the presence of a tri-reforming catalyst, to prepare a syngas, which then undergoes gas-phase direct synthesis into dimethylether in one step in the presence of a hybrid catalyst. According to the process of this invention, three main processes among typical syngas preparation processes are simultaneously performed, and then, the syngas thus obtained is prepared into dimethylether through a direct reaction in one step, thereby decreasing the apparatus cost and operation cost. In addition, all of the carbon dioxide separated and recovered from the unreacted material and by-products may be reused as reaction material, thus decreasing the generation of carbon dioxide and reducing the material cost.