The invention relates to a method for preparing large-grained SAPO-34 molecular sieves. The method comprises the following steps: batching in a gelatinizing tank, batching in a high-pressure crystallization kettle, stirring into gel, carrying out two-stage crystallization, separating, washing and drying and the like to prepare raw powder of the large-grained SAPO-34 molecular sieves. The large-grained SAPO-34 molecular sieves prepared by the method is used for MTO reaction, is good in hydrothermal stability and high in olefin selectivity, solves the problems of serious material loss in filtering and washing and poor hydrothermal stability and the like of the molecular sieves in the current industrial synthesis of the SAPO-34 molecular sieves, is environment-friendly and energy-saving and is easy to realize industrial large-scale production.