The invention discloses a micro 
optical fiber gas sensor covered by adopting 
graphene and relates to the field of gas sensors, in particular relates to the field of an 
optical fiber intermodal interference sensor. A micro 
optical fiber which is drawn to have two thick ends and thin middle through a fused biconical taper method is arranged on a 
magnesium fluoride substrate, a single-layer 
graphene material covers the middle section of the micro optical 
fiber, and because the single-layer 
graphene material is extremely sensitive to chemical bonds between atoms and an extranuclear 
electron state is extremely sensitive to an ambient environment, distribution of a 
dielectric constant is changed due to contact between the material and 
trace gas molecule, so that the optical 
refractive index is changed, and finally the intermodal interference spectrum of light propagated in the optical 
fiber is changed, the gas types are identified by detecting the interference spectrum, and the aims of the gas sensor are achieved. Therefore, the micro optical 
fiber gas sensor has the advantages of small size, high precision, high sensitivity, stability in operation and repeated utilization effect.