The mechanical properties of fiber Bragg Grating (FBG) strain sensors in ultra-low temperature environments are very important for structural health monitoring (SHM) in the aerospace field. In this paper, two kinds of FBG temperature sensors and strain sensors were fabricated by femtosecond laser technology and ultrasonic metallization packaging process. The strain transfer mechanism, microstructure behavior, and macroscopic mechanical properties of the FBG strain sensors were discussed in detail and the corresponding theoretical models were constructed.