In this paper, a Nafion-based methanol gas sensor for fuel cell vehicles is produced. The sensing electrode materials are a series of Pt-Cu alloys (the atomic ratios of Pt to Cu are 1:0, 2:1, 1:1, 1:2) supported on carbon fibers. The structure and morphology of the materials are characterized by XRD, SEM and TEM. The electro-chemical properties of the materials are tested by cyclic voltammetry (CV), Amperometric i-t Curve and alternating current impedance (A.C. Impedance) measurements. When the Pt-Cu atomic ratio in the alloy is 1:1, the material agglomeration phenomenon of the material is the weakest and the electrochemical specific area (ECSA) is the largest. The sensor made by this material exhibits the best sensing performance. The device has a response of -36 mu A to 500 ppm methanol and a sensitivity of 0.07 mu A/ppm. This device has good resistance to CO poisoning and has been verified by DFT theoretical calculations. The sensor operates at room temperature with high selectivity and humidity resistance. Therefore, the sensor has a good application prospect for fuel cell vehicle's methanol detection.