A optical fiber sensor based on modular interference is proposed to measure temperature， refractive index and axial strain. Waist-enlarged taper is formed at the splice point of a single-mode fiber and a double-cladding fiber， which is then cascaded with two long-period fiber gratings with different periods. Due to the mismatch of the mode fields， the higher-order cladding modes are excited，three resonance peaks are formed， which have different sensitivity responses to different parameters. Therefore， by demodulating the wavelength shift of the three resonance peaks and using the coefficient sensitivity matrix， temperature， refractive index and axial strain can be measured.The experimental results show that the sensitivity is 60.07 pm/℃， 6.47 pm/℃ and 103.83 pm/℃ in the temperature range of 25℃~75℃， the refractive index is in the range of 1.335 5~1.359 5， and the sensitivity is -56.64 nm/RIU， 34.02 nm/RIU and -214.84nm/RIU， the axial strain is in the range of 200~1 400 με， the sensitivity is -2.14 pm/με， -3.61 pm/με and -2.59 pm/με.The resolution is 1.29℃， 0.000 42 RIU and 21.42 με respectively. The sensor has high sensitivity， good linearity and other advantages， can be widely used in the field of multi-parameter measurement.