The invention relates to a method for preparing a P type molecular sieve by using coal ash as a raw material. The method for preparing the P type molecular sieve by using coal ash as the raw material comprises the following steps: I, pre-treating and activating coal ash; II, preparing sodium silicate and sodium metaaluminate by using activated coal ash; and III, synthesizing the P type molecular sieve: firstly, uniformly mixing a sodium silicate solution with a sodium salt, then, dropwise adding the sodium metaaluminate solution into the mixed liquid, and finally, adding an organic steric hindering agent and a proper amount of deionized water to form a reaction mixture, wherein the molar ratios of the reaction mixture are as follows: SiO2/Al2O3=0.4-1.8, M/Al2O3=1-5, Na2O/Al2O3=2-4 and H2O/SiO2=20-150 and the organic spatial steric hindering agent is at least one of ethanol amine, diethanol amine and triethanol amine; packing the mixed materials in a polytetrafluoroethylene container, stirring, then putting in a stainless steel reaction kettle, and carrying out hydro-thermal synthesis for 2-8 hours; and taking out products in the reaction kettle, carrying out centrifugal separation and washing by deionized water, and drying to obtain the P type molecular sieve. The method provided by the invention is short in synthetic cost, short in crystallization time and high in yield of the P type molecular sieve.