The invention relates to a method for transforming methyl alcohol into propylene, and mainly solves the problems of low finished propylene yield, low P/E (quality rate of propylene and ethylene) rate and poor hydrothermal stability of catalyst of the prior art. The invention takes methyl alcohol as raw materials and water as thinner. The raw materials reacts with the thinner through alumina catalyst bed at the temperature of 200 to 500 DEG C to generate a reaction effluent I at the reaction pressure of 0.01 to 0.1MPa, the space velocity of 0.5 to 10 hours<-1> when the methyl alcohol liquid ismultiplied and the mole rate of the water and the methyl alcohol of 0 to 5:1. The reaction effluent 1 is contacted with a ZSM-5 modified molecular sieve at the temperature of 400 to 600 DEG C to generate an effluent 2 which comprises propylene, wherein, the ZSM-5 modified molecular sieve adopts ZSM-5 modified molecular sieve primary powder, the weight proportion of which is 30 to 100 percent and the ratio of silicate to aluminum (Sio2AL2O3) is 20 to 1000, to be molded into strips with the rest adhesion agent which is selected from at least one of SiO2, clay or AL2O3, and then the strips are changed through ammonium solution which is selected from at least one of ammonium nitrate, ammonium chloride or ammonium sulphate, or acidic solution which is selected from at least one of hydrochloricacid, nitric acid, sulphuric acid, phosphoric acid or acetic acid; and then the invention is processed through water steam at the temperature of 400 to 700 DEG C.