In this paper, a rapid, facile and green strategy — electron beam irradiation has been developed to prepare CdSe nanoparticles. 10 mA GJ-2-II electronic accelerator was applied as radiation resource. CdSe nanoparticles were synthesized using NH3 as complexing agent by electron beam method in a colloid system, which used Cd(Ac)2 and Na2SeO3 as raw materials. Nanocrystalline CdSe was prepared rapidly at room temperature under atmospheric pressure. The structure and morphology of prepared CdSe nanoparticles were analyzed by X-ray diffraction and transmission electron microscopy. UV–vis spectroscopy (U-3010, Japan Hitachi) and photoluminescence spectroscopy (PL, F-7000, Japan Hitachi) were used to investigate the optical properties of the CdSe nanoparticles. The effects of radiation dose on the formation of CdSe nanocrystallines were discussed. The possible mechanism of the CdSe grain growth by electron beam irradiation method was proposed.