The invention relates to a synthetic method of methyl blocking polyether, which belongs to the technical field of alkyl blocking polyether preparation. The method comprises the follower steps: A: alcohol-salinization agent is added into polyether to perform a reaction, the alcohol-salinization agent is any of or the mixture of potassium hydroxide or sodium hydroxide; the reaction temperature is 50 to 150 DCG C, the reaction time is 05 to 4 hours, the feeding mol ratio of the polyether and the alcohol-salinization agent in a general formula (I) is 1:1-2, the pressure is minus 0.085 to minus 0.1MPa, and the water produced in the reaction is removed; B: monochloro methane gas is pumped into a pressure reaction still for continuous reaction, the temperature is 40 to 120 DEG C, the reaction time is 2 to 10 hours, and the pressure is 0.1 to 0.5 MPa; C: product refining: 1 to 5 percent of distilled water is added into the crude product in the condition of stirring, sodium chloride or potassium chloride becomes bulky crystals, so that the refined product can be obtained after filtration. The invention has reasonable industrial design, simple post treatment, no pollution, high yield and stable product quality.