The invention relates to a light hydrocarbon separation method used in a methanol to olefin device. According to the method, through the optimization for conventional technological processes, the recovery rate of ethylene and propylene can be effectively improved, meanwhile, other absorbents are not introduced, and materials such as ethane, propane and three-carbon mixture in a system are used to absorb; multi-section absrptions, namely, main absorption and auxiliary absorption are arranged, a main absorption liquid is short in circulation in the system, and can effectively reduce the system operation load and reduce the device running cost, the auxiliary absorption circulating process is relatively longer than that of the main absorption, but the circulation amount is small, and the influence on the system load is relatively small. Through the adoption of multi-stage absorption, the separation of gases of methane, hydrogen, nitrogen, oxygen, carbon monoxide, ethane and the like from ethylene, propene and propane can be realized without copious cooling. The loss of ethylene and propene in fuel gas is small, the separating efficiency is high, and fuel gas products with less propane can be obtained, propylene and ethylene products satisfying polymer grade requirements can be manufactured, and, meanwhile, propane products with high purity can be obtained.