An SnO2-WOs nanometer flowers coated microfiber bi-taper interferometer (MFI) for methane concentration detection is proposed and demonstrated. The tapered MFI is fabricated by fused bi-tapers method with the multi-core fiber. The methane sensitive materials SnO2-WO, is synthesized by using hydrothermal and impregnation methods. And the SnO2-WO3 material is coated on the MFI structure outsides by using the drop coating method.When the methane molecules is adsorbed on the coating material, the refractive index of the material will be changed, which will cause the transmission spectrum of the sensor changed. So, the methane concentration can be detected by measuring the wavelength shift of the spectrum. Experimental results show that the SnO2-WO3 nano-flower coated MFI sensor has large concentration detection range and high stability at room temperature. The measurement methane concentration range is 0~34%, the sensitivity is about 0.11 nm/%. The selectivity of the sensor is also studied. The responses of isopropyl alcohol, methanol, alcohol and methane are studied and compared,the results show that the sensor has high adsorption selectivity of methane, which has potential application in the field of mine gas detection and early warning.