In order to monitor interlayer pressures of connection structure with pre-tightening silicone foam cushion.A pressure sensing mode is proposed by using polarization-maintaining photonic crystal fiber (PM-PCF) as sensitive units and Sagnac interferometer,the sensitivity and pressure sensi ng characteristics of the sensor were validated by experiments.The influence of loaded length and loaded position of fiber on pressure sensing characteristics was analyzed,and a modification method of test data of PM-PCF sensor was provided.The results showed that the feasibility of the design.The test results show the accuracy of PM-PCF sensor can reach within 0.1‰,and the pressure sensitivity of PM-PCF sensor is related to loaded lengt h and loaded direction of fiber. When loaded direction is close to slow-axis of fiber,the PM-PCF sensor′s pres sure sensitivity can reach 0.4414nm/kN.By comparing the results of theoretical method,n umerical simulation and experimental measurement,the modification factors of the testing data from PM-PCF sensor is 1.14.Conclusion provides theoretical and test basis for the application and of fiber optic pressure senso r.