In this paper,a strain sensing characteristic of fiber Fabry-Perot (F-P) micro-cavity fabricated by hydrofluoric acid (HF) chemical etching method in ultra-low temperature liquid nitrogen environment was presented.The groove structure was obtained by corroding the end face of the single-mode fiber with a concentration of 20% HF solution for 15 min,and the corroded end was welded with the single-mode fiber with the other end face cutting flat to form flat an F-P micro-cavity.The F-P reflection spectrum contrast was 7.98 dB and the free spectrum range (FSR) was 17.8 nm.The fiber F-P sensor was pasted on the equal strength girder and placed in liquid nitrogen (-196 ℃) environment,and the strain range was 70—630 με in the experiment.The wavelength of F-P reflection spectrum drifted 4.21 nm in the short-wave direction,the strain sensitivity is -7.17 pm/με and the R-squared is 99.928% during the applied strain.The wavelength of F-P reflection spectrum drifted 4.33 nm in the long-wave direction,the strain sensitivity is 7.34 pm/με and the R-squared is 99.923% during the unloading strain.Through the hysteresis analysis of the ultra-low temperature strain response characteristic experiment,it is found that the maximum deviation of applied-unloading strain wavelength drift is 0.17 nm,which proves that the designed sensor has stability and reliability.