Based on the flexible structure design of photonic crystal fiber cladding air holes,the magnetic fluid-infiltrated ph otonic crystal fiber (MF-PCF) and common-PCF were w elded together.By etching Bragg grating in the fiber core area, a kind of PCF-Bragg grating sensors which can simultaneously measure temperatu re,magnetic field and strain is put forward.Based on mode coupling theory and transfer matrix method ,combining different sensing properties of core mode and higher-order mode in PCF,the resonance wavelength-shift characteristics are carried out by analyzing the influence of thermal effect, magneto-optic effect and elastic-optic effect on Bragg grating.The experimenta l resul ts show that,the sensor has high sensitivity response to temperature,magnetic field and strain,an d the resonant wavelength-shift has a good linear relationship with temperature,magnetic fiel d and strain.The highest temperature sensitivity can reach 13.97pm/℃,the magnetic field sensitivity is 10.04pm/mT,and the strain sensitivity is 1.223pm/με.Through d esigning appropriate three-parameter matrix demodulation algorithm,we can reali ze the measurement of temperature,strain and magnetic field simultaneously,and this method can effecti vely reduce the cost of sensor and broaden the sensing approach.