The invention discloses a method for preparing Mg<2+>-doped basic nickel carbonate microspheres. The method is implemented bythe following steps: 1) separatingpreparing a carbonate solution and a nickel salt solution; 2) adding the two solutions to a reactor at the same time, controlling the pH value of the system to 7.9-8.3, performing a reaction for 1-2 hours, and performing concentration treatment on the reaction solution so as to obtain basic nickel carbonate slurry; 3) performing filter pressing on the basic nickel carbonate slurry to remove mother liquor, further performing pulping, transferring the pulped material into a reaction kettle, further adding an ethanol aqueous solution of magnesium salt, and performing a stirring reaction so as to obtain Mg<2+>-doped basic nickel carbonate slurry; and 4) washing the slurry, and performing high-temperature drying, so as to obtain a target material. The preparation process of the method is simple and feasible, and in addition, as lattice defects are formed after Mg<2+> doping, the electron separation efficiency can be promoted, and the prepared Mg<2+>-doped basic nickel carbonate microspheres have photocatalytic performance which is3 times or higher than that of ordinary basic nickel carbonate.