Abstract: In order to study the polarization property of a laser radiation side-scattered by randomly distributed particles in different diameters, various concentrations of suspending liquid, consisting of distilled water and particles in diameters of 0.22μm or 0.494μm, was served as the scattering medium. Through theoretical analysis and experiments, the data of polarization degree in different depths and at different angles scattered by 0.22μm particles were acquired,and the data of horizontal polarization and vertical polarization scattered by 0.22μm and 0.494μm particles in three different concentrations of suspending liquid were also obtained respectively. The experiment results show that the de-polarization of radiation side-scattered by the particles is very sensitive to the variation of the diameters of the particles,i. e.,the horizontal polarization degree of the radiation scattered by the particles in smaller diameters is much higher than that scattered by the particles in larger diameters. However,it is inverse for the vertical polarization degree. The result is helpful to test the diameter of particles under the condition of multiple particles (especially for the particles'diameter less than 1μm).