The present invention relates to a method for preparing 2,3-dimethyl-2,3-dinitrobutane (DMNB), which includes the following steps: (1) making titanium-silicate molecular sieve catalyst, acetone, hydrogen peroxide and ammonia contact and react at 65-80° C. to obtain a modified titanium-silicate molecular sieve catalyst; and (2-1) making acetone oxime and hydrogen peroxide contact and react in the presence of the modified titanium-silicate molecular sieve catalyst and water under the conditions of temperature of 60-90° C. and pH of 8-10, and separating DMNB from the reaction products thereof; or (2-2) making acetone, ammonia and hydrogen peroxide contact and react in the presence of the modified titanium-silicate molecular sieve catalyst and water under the conditions of temperature of 60-90° C. and pH of 8-10, and separating DMNB from the reaction products thereof. By the method provided by the present invention, DMNB can be prepared without having to use dangerous chemicals, such as 2-nitropropane, NaH and the like.