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 is 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 to form an F-P micro-cavity. The F-P reflection spectrum contrast was 7.98 dB and the free spectrum range was 17.8 nm. The optical fiber F-P sensor was pasted on the equal strength girder and placed in liquid nitrogen environment (-196 ℃), 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 strain application; 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 process. Through the hysteresis analysis of the ultra-low temperature strain response characteristic experiment, it is found that the maximum deviation of applied-unloaded strain wavelength drift is 0.17 nm which proves that the designed sensor has stability and reliability.