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This paper firstly and experimentally demonstrates an in-fiber axial micro-strain sensing head,combined with a Mach-Zehnder interferometer (MZI) based on the concentric multilayer elliptical-core fiber (CMECF).This MZI with a high extinction ratio (about 15 dB) is successfully achieved with a CMECF-single mode fiber-CMECF (CSC) structure.The MZI sensor theory and the resonance demodulation technology are systematically described in this paper.In this CSC structure,two sections of the CMECF have a role as the mode generator and coupler,respectively.LP01 and LP11even,which have similar excitation coefficients,are two dominated propagating mode groups supported in the CMECF.On account of the distinct dual-mode property,a good stability of this sensor is realized.The detected resonance in the MZI shifts as the axial micro-strain variated due to the strong interaction between higher order modes.High sensitivity of ～1.78pm/με is experimentally achieved within the range of 0με-1250με,meanwhile,the intensity fluctuation is below 0.38dB.