The invention relates to a preparation method of a MnO2 catalyst for further mineralizing phenolic waste water at normal temperature, which belongs to the technical field of thermal catalytic materials. The preparation method comprises the following steps: firstly mixing potassium permanganate and reducing adjuvant to obtain turbid liquid, reacting for 10 to 15 hours at the temperature of 180 to 250 DEG C, naturally cooling, thus obtaining the MnO2 catalyst with further mineralization capacity. The MnO2 catalyst prepared by the method of the invention has excellent activity for further mineralizing the phenolic waste water; and moreover, the preparation method provided by the invention is cheap in raw materials and simple, thereby effectively decreasing the product cost, having great environmental protection value, and having high practical value and application prospect.