The invention relates to a method for preparing large granular praseodymium neodymium oxide by precipitating ammonium hydrogen carbonate at normal temperature. The method is characterized by comprising the following steps: adding a praseodymium neodymium chloride solution with a concentration of 0.2-0.8 mol/L into a reactor, and directly adding an ammonium hydrogen carbonate solution with a concentration of 1-3 mol/L into the praseodymium neodymium chloride solution at normal temperature, wherein the molar ratio of praseodymium neodymium chloride to ammonium hydrogen carbonate is 1: (3.2-4); adding the ammonium hydrogen carbonate solution in two steps, firstly adding a part of ammonium hydrogen carbonate solution in the first step, stewing and aging for 10-15 hours, adding the rest ammonium hydrogen carbonate solution until complete precipitation, wherein the pH is 6.2-6.5; aging for 10-15 hours at normal temperature, filtering, washing with hot water, and naturally drying to obtain praseodymium neodymium carbonate precipitate with 8 crystal water, roasting the praseodymium neodymium carbonate precipitate to obtain a large granular praseodymium neodymium oxide product with a median particle diameter of 30-40 microns. The method has the advantages that the stepped aging manner is adopted to increase the median particle diameter of the praseodymium neodymium oxide from 1-2 microns to 30-40 microns, so as to greatly improve the granularity of the praseodymium neodymium oxide, and meanwhile, no heating treatment is needed in the precipitating process, so that the production cost is reduced.