A refractive index (RI) sensor based on elliptical core photonic crystal fiber (EC-PCF) has been proposed.The asym-metric elliptical core introduces the polarization-dependent characteristics of the fiber core modes.The performances of intermodal interference between the intrinsic polarization fiber core modes are investigated by contrast in two inter-ferometers based on the Mach-Zehnder (M-Z) and Sagnac interference model.In addition,the RI sensing characteris-tics of the two interferometers are studied by successively filling the three layers air holes closest to the elliptical core in the cladding.The results show that the M-Z interference between LP01 and LP11 mode in the same polarized direc-tion is featured with the incremental RI sensing sensitivity as the decreasing interference length,and the infilled scope around the elliptical core has a weak correlation with the RI sensing sensitivity.Due to the high birefringence of LP11 mode,the Sagnac interferometer has better RI sensing performance,the maximum RI sensing sensitivity of 12000 nm/RIU is achieved under the innermost one layer air holes infilled with RI matching liquid of RI=1.39 at the pre-setting EC-PCF length of 12 cm,which is two orders of magnitude higher than the M-Z interferometer with the same fiber length.The series of theoretical optimized analysis would provide guidance for the applications in the field of biochemical sensing.