The invention provides a method for preparing high-purity molybdenum trioxide from molybdenum concentrate through hydrometallurgy. The method comprises steps as follows: the molybdenum concentrate anddeionized water are mixed uniformly, and molybdenum concentrate pulp is prepared; the molybdenum concentrate pulp is subjected to a high-pressure oxygenolysis reaction, the reacted pulp is filtered;an obtained filter cake is subjected to alkaline leaching, filtered and washed, and a molybdate solution and waste residues are obtained; obtained filtrate and the molybdate solution are mixed, alkaliis added to adjust the pH, and the mixture is precipitated for impurity removal; the pH of a solution obtained after filtration of precipitates is adjusted to be neutral, a precipitation aid is addedand mixed sufficiently, and sulfuric acid is continuously added for pH adjustment, and acid settlement is performed; a material subjected to acid settlement is filtered again, a filter cake is calcined, and the high-purity molybdenum trioxide is obtained. The molybdenum content of the high-purity molybdenum trioxide obtained with the method can reach 66% or above, the total recovery rate of molybdenum can reach 98% or above, and meanwhile, raw gypsum products can be produced. The method is a production process which cannot cause environmental pollution, adopts a simple technological process and is used for preparing the high-purity molybdenum trioxide.