With CW (continuous wave) laser and a high-speed CCD,hologram of alcohol spray is recorded based on digital in-line holography arrangement.The reconstruction images of a hologram of the particle field are handled the way that in-focus images of the particles in the volume are integrated into a plane and binarized and the edge of the particle images is extracted by Roberts,then Hough transform and sub-pixel precision computing completed,and the size and position of the particles are obtained.The displacement of the particle is extracted by two sequences of the hologram recorded by two exposures and the velocity of the particle is obtained,and the experimental results are given.The research results show that the proposed experimental system is applied to measuring internal combustion engine spray field,which is simple in optical structure and low in cost.