In order to develop a methane sensor with low-cost and excellent sensitive characteristics,a fiber-core mismatched type methane sensor based on Cryptophane E was designed. The sensitivity of the fiber-core mismatched methane sensor with different lengths of Cryptophane E coating to various concentration mixed methane gas was measured. Optical power versus injection angle for the methane sensor with the best sensitive coating length in pure nitrogen and 12% mixed methane gas were measured respectively. In order to find out the best injection angle,the difference of optical power in pure nitrogen and 12% mixed methane gas were calculated as well. Results showed that the best sensitive coating length is 3 mm,and the maximum optical power difference emerges when the injection angle is at θ=1°. The lowest detection limit of the fiber-core mismatched methane sensor is 2.3%. The optical power increases with the increasing of methane gas concentration.