Provided is a method for preparing manganese sulfate monohydrate, which comprises the following steps: (1) adding equimolar BaS or SrS solution into manganese sulfate solution to carry out reaction fully, and separating and washing the obtained solid; (2) mixing the solid with deionized water to prepare a slurry, dissolving the slurry with concentrated sulfuric acid, and separating solid from liquid to obtain MnSO4 solution; (3) adding proper amount of hydrogen peroxide to the MnSO4 solution, heating to boiling, adjusting the pH value of the solution within 5-6, evaporation the filtrate after a precise filtration, and crystallizing and drying to obtain MnSO4 H2O product. Manganese sulfate monohydrate can be produced at high yield in a cost-efficient manner by this method.