The invention provides a method for preparing a nitrate and magnesium sulfate mixed product from manganese-contained waste liquid. The method comprises the following steps of: carrying out suction filtration to manganese-contained waste liquid obtained in the production of hydroquinone to obtain a clear filtrate containing manganese sulfate, ammonium sulfate and sulfuric acid and a filter cake containing elemental residues; making the filter cake containing elemental residues react with superfluous sulfuric acid to obtain a solution containing calcium sulfate, magnesium sulfate, zinc sulfate, sodium formate, aluminum sulfate, cadmium sulfate and nickel sulfate; carrying out a hybrid reaction with a magnesium nitrate solution to obtain a mixed solution containing the magnesium sulfate and the nitrate of calcium nitrate, zinc nitrate, sodium nitrate, aluminum nitrate, cadmium nitrate and nickel nitrate; and filtering to obtain a calcium nitrate filter cake and a filtrate containing nitrate and magnesium sulfate, washing, drying and crushing the calcium nitrate filter cake to obtain a calcium nitrate product and decompressing, distilling, cooling and crystallizing the solution containing nitrate and magnesium sulfate to obtain a nitrate and magnesium sulfate mixed product.