The deformation behavior of near-β Ti-5553 alloy under the impact of light gas gun has been studied by optical microscopy (OM) combined with quantitative metallographic analysis, transmission electron microscope (TEM) and X-Ray Diffraction (XRD). The experimental results demonstrated that Ti-5553 alloy deform via dislocation slipping，deformation twinning and stress-induced martensite (SIM) phase transformation. Meanwhile, the amount of SIM is influenced by the velocity of flyer plates by which Ti-5553 alloy was impacted. The amount of SIM increased obviously as the impact velocity increased. Particularly, when the velocity increased from 380m/s to 560m/s, the length of the SIM wire per unit area (LA) increased from 39.18mm/mm2 to 52.65 mm/mm2.