NOVELTY - Preparing nitrogen-phosphorus-potassium compound fertilizer by using black mica involves: (1) adding 20-200 mesh black mica mineral powder into sulfur acid leaching solution in 1:1-1:5 ratio at 60-140 degrees C under normal pressure for 1-10 hours, taking out and cooling to the room temperature to obtain the solid substance, adding water, filtering to obtain filter slag and filter liquid A; (2) adding ammonia into the liquid for neutralization to obtain the mixed deposit and filter liquid B; and (3) evaporating the liquid B for crystallization.    USE - For preparing nitrogen-phosphorus-potassium compound fertilizer (claimed).    ADVANTAGE - The preparation method is simple and easy to operate with short working process. The method in a relatively mild condition uses black mica to prepare potassium sulfate, ammonium sulfate and ammonium magnesium sulfate to create initially the new method for making nitrogen-phosphorus-potassium compound fertilizer.    DETAILED DESCRIPTION - Preparing nitrogen-phosphorus-potassium compound fertilizer by using black mica, involves: (1) acid dipping: adding the 20-200 mesh black mica mineral powder into sulfur acid leaching solution, where the reaction temperature is 60-140 degrees C, dipping under the normal pressure for 1-10 hours, taking out and cooling to the room temperature to obtain the solid substance; adding water (twice the mass of the solid substance) for dilution to the solid substance of 2-20 folds, then filtering to obtain the filter slag and the filter liquid A; where the mass ratio of the black mica mineral powder to the sulfuric acid leaching solution is 1:1-1:5; (2) ammonia neutralization: adding ammonia into the liquid for neutralization when stirring the liquid, then filtering to obtain the mixed deposit of the magnesium hydroxide, ferric hydroxide, ferrous hydroxide, aluminum hydroxide and the filter liquid B containing potassium sulfate, ammonium sulfate and ammonium sulfate; and (3) evaporation and crystallization: evaporating the liquid B for crystallization, adding substance containing phosphorus in the crystallization product, processing the nitrogen-phosphorus-potassium compound fertilizer with regular processing method; where the mass ratio of the crystal product to the phosphorus-containing matter is 1:0.1-1:5.