The invention discloses a new method for preparing natural nucleoside nebularine. According to the method disclosed by the invention, cheap inosine is used as a raw material and is subjected to three reactions including acyl protection, sulfuration and desulfuration to finally obtain the target product nebularine; in the desulfuration step, since 50% nitric acid is used as a desulfuration agent, such reaction conditions easily causing explosion as diazotization in the conventional synthesis method can be avoided, no heavy metal catalyst is used, no column chromatography is needed in the whole process, large-scale synthesis can be realized easily; and moreover, the new method for preparing natural nucleoside nebularine is suitable for research on medicine activity and further large-scale preparation.