The invention discloses a method for preparing and purifying graphene by microwave radiation under vacuum. The method for preparing graphene is as follows: placing graphite oxide in a reactor, radiating the graphite oxide by microwaves under vacuum, and obtaining the graphene by heating and cleavage of the graphite oxide. The method for purifying graphene is as follows: placing graphene with low purity in a reactor, irradiating the graphite oxide by microwaves under vacuum, and obtaining the graphene with higher purity after impure graphene is subjected to heating and cleavage. The method is implemented under the vacuum condition, thus being favor to preventing the generated graphene from being oxidized by oxygen in the reactor, reducing the cleavage resistance of the graphite oxide, and ensuring the safety in the operation process, and the method also has the advantages of high production efficiency, low production cost, safe operation process, high product purity and the like, and can be used as one of the methods for preparing and purifying graphene massively.