A fiber-optic pressure sensing system based on panda polarization-maintaining fiber（ PMF）-Sagnac loop structure is proposed. Taking the advantage of sensitivity of birefringence of PMF to external environment and can performs narrow-band filtering

set up pressure sensing system

and demodulation of the sensing system is performed. The proposed system has advantages of simple structure

low cost and easy to operate. Theoretical analysis shows that when the sensing unit is fixed

as the pressure increases

the wavelength drift of interference light of sensing system change linearly. The experiment verifies the characteristics of pressure sensing with the length of the sensor probe is 1 m and 2 m

respectively. The experimental results show that with the increase of pressure

the wavelength of the sensing system changes linearly

the linearity is 0. 998 and 0. 995

respectively.Meanwhile

the sensitivity is 0. 258 nm/N and 0. 133 nm/N

respectively. And with the length increasing of sensing fiber

the 3 d B bandwidth of the transmission spectrum trough remain constant.