The invention relates to the bio-manufacturing field and particularly relates to a construction body for producing carbohydrate compound by virtue of synechococcus UTEX2973, a strain and a method. The construction body contains a promoter, a proton/saccharose synergetic transport protein gene, an antibiotic resistance gene and a homologous arm, wherein the promoter has activity in synechococcus UTEX2973, the proton/saccharose synergetic transport protein gene is controlled by the promoter, the antibiotic resistance gene is used for screening a transformant, and the homologous arm is used for homologously integrating genomes. The carbohydrate compound is synthesized by immobilizing carbon dioxide by virtue of solar energy in a photosynthetic microorganism, namely cyanobacteria, the energy for synthesizing carbohydrates is from the solar energy, and a carbon source is from carbon dioxide. Therefore, a biology base product prepared by virtue of the method is not restricted by insufficient raw materials, the carbon emission is not increased during the use of the biology base product, and the biology base product is a true zero-emission biology base product.