The invention discloses an SAPO-34 molecular sieve adjustable in micropore diameter and a preparation method and application of the SAPO-34 molecular sieve adjustable in micropore diameter.The preparation method includes adding inert organic solvents into an SAPO-34 molecular sieve, adding easily-hydrolytic halide as a precipitant, and reacting for 2-10 hours prior to filtering, drying and roasting so as to obtain the SAPO-34 molecular sieve adjustable in micropore diameter.The SAPO-34 molecular sieve adjustable in micropore diameter is applied to MTO (methanol to olefins) for preparing low-carbon olefins from oxygen compounds by conversion.Compared with a silicon esterification deposition method and the like, an SAPO-34 micropore diameter adjusting method has the advantages of simplicity, low price, repeatability, reliability, wide applicable range, suitability for industrialization and the like.After adjustment by the SAPO-34 micropore diameter adjusting method, zeolite pore volume and inner surface properties are unchanged but orifice size is adjustable precisely, and accordingly the SAPO-34 molecular sieve demonstrates excellent shape selecting and separating properties for various organic matter mixture systems diverse in geometric dimension and close in polarity and can be used for separating and purifying organic chemical reagents.