The present invention relates to a method for producing chlorine dioxide with high purity by adopting a combined reducing agent. The method comprises the following steps of: injecting concentrated sulfuric acid and a sodium chlorate solution into a generator to form a reacting mother solution; maintaining the reacting mother solution to a certain acidity, temperature and the content of sodium chlorate; then adding a combined reducing agent comprising methanol, hydrogen peroxide, hydrochloric acid or sodium chlorate to react for generating chlorine dioxide gas and a byproduct namely acid mirabilite; cooling and then absorbing the chlorine dioxide gas by using low temperature frozen water to obtain a water solution of chlorine dioxide; and simultaneously recovering the byproduct. The conversion rate of the chlorine dioxide produced by the method is improved by 3-6 percent as comparison with that of the chlorine dioxide produced by a single reducing agent, the stability of chemical reaction is improved, the production cost is reduced, and the chlorine amount in the chlorine dioxide solution and tail gas exhausted from a chlorine dioxide absorbing tower is remarkably reduced.