Cadmium sulfide nano-particles have been successfully prepared by electro beam irradiation in the water system. The products were characterized by X-ray diffraction, transmission electron microscope and fluorescence spectroscopy. The results indicated that the CdS nano-particles were of pure face-centered cubic crystal and in spherical shape of, averaged about 15nm in size. The UV absorption edge of CdS nano-particles is 487nm. When the excitation wavelength was 350nm, the peak of the emission wavelength of CdS nano-particles is at 476nm, and the fluorescence was attributed to the emission of band edge. The influence of the concentration of PVA on the size of the CdS nano-particles was studied by laser scattering particle size distribution analysis. The results showed that the size of the CdS nano-particles decreased with increasing the concentration of polyvinyl alcohol during a certain extent.