Abstract: An exploding foil initiator was designed. The question of the velocity measurement of small-size flyer was effectively solved by adopting the measures as follows: (1) accurately control the orientation of bridge foil, flyer and barrel; (2) put a thin aluminum film on the surface of the flyer and the mass of the aluminum film can be neglected compared with that of the flyer; (3) reasonably choose the work distance of the VISAR probe and the fringe constants related with the time delay of interference cavity; (4) shield measuring system and use the optical filter. The velocity measurement results of the flyers with two different sizes of 0.7 mm0.025mm and 0.5 mm0.025 mm were given. Compared with the results by Weingart R C, the obtained results after taking the measures above are with good signal-to-noise ratios, and can reflect the physical essence of exploding foil initiator driving flyer.