The invention belongs to the field of industrial waste liquid treatment, and particularly relates to a waste liquid treatment method in a guanine preparation process. Sulfuric acid and alcohol substances are added into a closed-loop reaction liquid generated in the process of producing the guanine step by step, the conversion between sodium formate and formic acid in the closed-loop reaction liquid is realized, the formate and salt substances obtained after conversion are recycled, so that the economic value of the wastewater in the production process of the guanine is effectively improved, and the pollution to the environment is reduced.