Abstract: It is important to study liquid particle size in the dispersion in civil and military affairs range. Up to now it is the first time for the liquid particle size in the dispersion to be measured in our country using laser scattering apparatus, under explosive detonation. Based on the analysis on the interaction law between laser and liquid particles and the technique of measuring liquid particle size used by R. A. Dobbins et al, a set of simple and practical apparatus (i. e. laser scattering apparatus) has successfully developed to determine the liquid particle size in the secondary breakup of the fuel dispersion in this paper. For the interaction of laser with liquid particles, we have derived the light intensity formula of scattering on condition of neglecting the effects of reflection and refraction of light and absorption of light. This light intensity formula of scattering allows us to measure the Sauter mean diameter of liquid particles. In our experiment of measuring the liquid particle size in the process of the fuel dispersion, we substitute the explosively dispersed liquid with water. The experimental results show that during the secondary breakup of the liquid dispersion the Sauter mean diameter of liquid particles measured at the fixed position in the atomization area becomes smaller as time increases, the width of the atomization area becomes larger as the distance from the center of the fuel dispersion increases, and the Sauter mean diameter of particles in the front of atomization area decreases rapidly after increasing gradually as the distance increases. To be compared with other experimental results, the liquid particle size has been measured by the recovery method, and a numerical simulation of the secondary breakup of the liquid dispersion has also been performed. The obtained results are in a good agreement with those measured using laser scattering apparatus.