The invention discloses a preparation method of a high activity SAPO-34 molecular sieve. According to the method, a directing agent subjected to room temperature pressurization aging is added into a synthetic crystallization liquid to prepare a high activity SAPO-34 molecular sieve, wherein the directing agent is prepared by: at room temperature, filling a high pressure crystallization kettle loaded with crystallization liquid with gas, performing aging for a period of time under certain pressure, and then conducting emptying. The method provided by the invention prepares the directing agent through pressurization aging, preparation is carried out under room temperature, the operation is convenient and the cost is low, thus being convenient to realize industrial mass production. The appearance of the SAPO-34 molecular sieve prepared by the method is a quadrel structure falling in between a slice and a cube, and the particle size is about 1.3 micrometers, specifically the quadrel structure is more beneficial to diffusion of a reaction product in catalytic reaction, thus having high activity to MTO reaction, and being able to effectively prolong the life of a catalyst. The SAPO-34 molecular sieve prepared by the method provided by the invention has a large crystalline grain, and the product is to separate, therefore the yield is high, and the production cost is lower.