The invention discloses a method for preparing a magnetic P-type molecular sieve by using coal gangue. The method comprises: 1, grinding coal gangue, and carrying out high temperature calcining activating on the grinded coal gangue by using sodium carbonate; 2, oxidizing at a low temperature, adding hydrochloric acid, soaking, and filtering; 3, preparing an iron-doped molecular sieve from the filtration residue and the filtrate obtained after the filtration; and 4, placing the iron-doped molecular sieve in a porcelain boat, placing the porcelain boat in a tubular furnace, introducing nitrogen into the tube furnace, introducing hydrogen after the air in the tubular furnace is completely discharged, heating to a temperature of 650-700 DEG C, continuously carrying out a reduction reaction for 2-3 h, introducing nitrogen after completing the reaction, and cooling to a room temperature to obtain the magnetic P-type molecular sieve. According to the present invention, the coal gangue is used as the raw material, the Fe<3+> dissolution is performed with hydrochloric acid and is complexed by adding oxalic acid, and finally high temperature reduction is performed to prepare the magnetic P-type molecular sieve; the magnetic P-type molecular sieve has characteristics of high specific surface area and strong adsorption performance; and the magnetic P-type molecular sieve is easy to separate and recover through the external magnetic field, and the problem of high cost of the molecular sieve synthesis is solved.