The present invention relates to a preparation method for forming a doped nanometer zinc oxide light conversion agent from a metal salt and a zinc salt under the effect of a reduction agent. The preparation method mainly comprises metal salt and zinc salt combination, metal salt and zinc salt ratio regulation, reaction temperature regulation, and other steps. According to the present invention, the light conversion agent can absorb one light having one wavelength in sunlight to convert into another light having another wavelength; the doped nanometer zinc oxide light conversion agent prepared through the soft chemical method has characteristics of simple operation, low price and excellent light conversion performance, and can be used in production in a large amount manner; and compared with other rare earth metal light conversion agents, the doped nanometer zinc oxide light conversion agent of the present invention has the stable light conversion performance.