In order to develop the laser interferometer velocimetry in the experimental research of shock wave physics and explosion physics, an allfiber velocity interferometer is presented. The singlemode fiber is adopted as optical transmission and delay components for this interferometer, which detects Doppler beat signals caused by velocity change to two moments of t and t－τ. Because of little velocity change of objects to be tested corresponding to twobeam optical signals of two moments, which almost have equivalent frequency shift, and the beat frequency is also significantly lowered. Meanwhile, the fringe constant (value τ) can be flexibly adjusted in accordance with velocity change rate of objects to be tested, thereby making the beat signal frequency caused by velocity change less than the system bandwidth within the time scale of τ, so as to solve the problem of recording system corresponding to bandwidth limitation and extend upper limit of velocity measurement. As result of the adoption of singlemode fiber, only one space pattern in the fiber participates in interference, even the light returned from diffusereflection surface can preferably participate in interference after the mode selection of singlemode fiber, thereby realizing the measurement to diffusereflection target. Two fringe constants of 1.5 m·s－1 and 150 m·s－1 are adopted to conduct the Hopkinson bar experiment at lowvelocity process and laserdriven experiment at highvelocity process. The experimental result proves the feasibility of this interference technique.