The invention relates to a method for nano-selenium through two-step solid phase synthesis, which belongs to the technical field of nano materials. The developed novel preparation process for red nano-selenium through the two-step solid phase synthesis comprises the following steps: obtaining nano effect of a precursor by a first step solid phase reaction; decreasing activation energy of a second step solid phase reaction; controlling nucleation rate; and realizing the control of the size of grain diameter of the nano-selenium, in which the grain diameter of the nano-selenium is controlled to be between 10 and 30 nm; and reducing the cost greatly. The synthetic process of the process has the advantages of environmental protection, less energy consumption, no discharge of three wastes, and no pollution; and by adding an inert carrier, the stability of the nano-selenium is improved, and the nano-selenium is dispersed uniformly. A final byproduct of the two-step solid phase synthesis is non-hazardous to human and animals, and a mixture needs not washing and separating so as to solve the problems of dispersion and aggressiveness of the nano materials in the process of washing and drying. The method provides technical support for fundamental research for promoting the nano-selenium as a feed additive and development of nano-selenium health care products, and is suitable for industrial production.