NOVELTY - The tank has a separating plate, an air electrode and a fuel electrode. The air electrode and the fuel electrode are respectively utilized for receiving effluent and mixed fuel. The air electrode is connected with an inlet and an effluent gas discharging part. The mixed fuel is passed to the fuel electrode through a raw liquid inlet and a mixed fuel supplying part. Upper and lower parts of the separating plate are respectively provided with a gas delivery part and a water supply channel. A porosity flux prevention plate is located at an innerside of a room.    USE - The fuel mixing tank is useful in a direct methanol fuel cell system (claimed).    ADVANTAGE - The tank is partable, and has excellent mixing stability, and minimizes rolling effect of the mixed fuel during vibration.    DETAILED DESCRIPTION - The tank has a separating plate, an air electrode and a fuel electrode. The air electrode and the fuel electrode are respectively utilized for receiving effluent and mixed fuel. The air electrode is connected with an inlet and an effluent gas discharging part. The mixed fuel is passed to the fuel electrode through a raw liquid inlet and a mixed fuel supplying part. Upper and lower parts of the separating plate are respectively provided with a gas delivery part and a water supply channel. A porosity flux prevention plate is located at an innerside of a room. The porosity flux prevention plate has honeycomb structure. The honeycomb structure has cell size of 2-12 mm and thickness of 3-100 mm. The gas delivery part is fixed with a porosity hydrophobicity separation film having pore size of 0.001-0.05 mm and thickness of 0.01-0.1 mm. A level sensor is placed in the room for sensing water level, where the water level is maintained lower than the fuel level according to the ratio of 1/10 to 1/3. A cross-sectional area of the water supply channel is 30 times the area of the gas delivery part. The area of the gas delivery part is 0.5-15 mm2. The cross-sectional area of the water supply channel is 1/5 times smaller than the area of the separating plate. An INDEPENDENT CLAIM is included for a direct methanol fuel cell system.