The invention relates to a method for improving yield of ethylene and propylene, which solves the problem of low yield of ethylene and propylene during lower olefins preparing process from conversion of methanol and dimethyl ether. The invention uses at least one of methanol and dimethyl ether and C4 hydrocarbon as materials, the materials enter into a reaction region from a distributor at the bottom of a fluidization bed reactor or from at least a position axially separated along the reaction region, and contact and react with a catalyst to generate an effluent containing ethylene, propylene and C4 hydrocarbon, the effluent is separated to obtain ethylene, propylene and C4 hydrocarbon; wherein, the C4 hydrocarbon material is from fresh mixed C4 hydrocarbon or mixed C4 hydrocarbon obtained by separation or mixtures thereof. In this way, the invention solves the problem well, and is useful in industrial production of ethylene and propylene.