Digital Particle Image Velocimetry (DPIV) is a new technology of fluid velocity measurement developed recently , and it has gain more and more attention. This paper expounds the basic principles of DPIV, and develops a set of DPIV measurement system, which is used to study the fuel spray. The system contains a transparent glass vessel, a flexible high powered light guide, a precise X - Y reference frame and a synchronous signal control device which can accurately control the action of the nozzle, the laser system and the CCD camera. Using this system, the whole fuel spray field can be observed from beginning to end. The results of diesel spray experiment show the entrainment phenomenon between surrounding gas and diesel spray, and the vortexes appear in parts of the atomizing area.