Abstract: Provided are a method for preparing starch using carbon dioxide, a recombinant microorganism, a method for constructing the recombinant microorganism, and a reagent. The method for preparing starch using carbon dioxide comprises: (1) providing energy and carbon sources for microbial cells on the basis of carbon dioxide and extracellular non-optical energy; and (2) generating starch within the microbial cells on the basis of at least one of up-regulated glucose-1-phosphate adenylyltransferase and starch synthase in the microbial cells. In this way, by utilizing non-optical energy, such as electric energy or hydrogen energy, starch can be effectively prepared inside the microbial cells by fixing carbon dioxide.