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A temperature insensitive refractive index sensor with a core-offset polarization-maintaining photonic crystal fiber interferometer (PMPCF) interferometer is demonstrated. The cladding modes can be effectively excited by core-offsetting one splice joint between the single mode fiber (SMF) and PMPCF in a SMF-PMPCF-SMF structure. When the cladding modes propagate to the other splice joint of the interferometer, an inter-modal interference between the excited cladding modes and the core modes can be constructed. As ambient refractive index changes, the transmission spectrum will experience corresponding wavelength shift. Experimental results show that a wavelength shift of 42.824nm is observed when the RI changes from 1.36 to 1.428. The sensor exhibits the advantages of simple structure, small size, high sensitivity, and temperature insensitiveness.