The invention discloses a metal modified SAPO-34 molecular sieve, and a preparation method and application thereof. The preparation method comprises adding a tungsten source and an SAPO-34 molecular sieve into a solvent, performing ultrasonic and microwave treatment, drying and roasting to obtain the tungsten modified SAPO-34 molecular sieve, wherein the tungsten source is a soluble tungsten source or an insoluble tungsten source; or mixing an aluminum source, a phosphorus source and deionized water into liquid A, mixing a main template agent and a silicon source into liquid B, mixing the liquid A and the liquid B, adding a tungsten source template agent, performing dynamic crystallization, drying and roasting to obtain the tungsten modified SAPO-34 molecular sieve; or mixing an aluminum source, a phosphorus source and deionized water into liquid A, mixing a main template agent and a silicon source into liquid B, adding the liquid B into the liquid A, performing dynamic crystallization, adding a tungsten source template agent and performing secondary crystallization to obtain the tungsten modified SAPO-34 molecular sieve. The molecular sieve prepared by the method can realize low-carbon alcohol and C4 olefin conversion process at the same time in the same reactor, produces ethylene and propylene highly selectively, reduces the yield of C4 olefin and increases the utilization rate of low-carbon alcohol.