The invention provides a preparation method of controllable and visual chlorine dioxide slow-release gel, and relates to the technical field of gas sterilization and deodorization. The method comprises the steps of respectively dissolving water-soluble materials including sodium chlorite, acrylamide, bisacrylamide, borax, potassium persulfate and the like, mixing in proportion, carrying out split charging, then feeding tetramethylethylenediamine, and carrying out polymerization reaction to obtain the polyacrylamide gel. When the controllable and visual chlorine dioxide slow-release gel is used, a matched acidification rod is inserted into the gel, and chlorine dioxide gas can be slowly released, so that the effects of sterilization and deodorization for the surrounding environment can be achieved. The method has the characteristics that the slow-generation and slow-release speed of the chlorine dioxide can be controlled by controlling the concentrations of the gel and the borax, the degree of crosslinking of the gel and the type of the acidification rod; the gel at the rear end of the product is formed by polymerization and is colorless and transparent, thus being suitable for various shapes; after the product is acidized and activated, the gel becomes yellow from colorless, the chroma of the gel is in direct proportion to the concentration of the chlorine dioxide, and vice versa, so that the gel also has the function of ClO2 indicator; after the product is acidized and activated, the released gas does not contain toxic by-product chlorine.