The invention belongs to the technical field of energy utilization, and especially relates to a separation system and a method of methanol to aromatics by-product liquefied gas. The separation system comprises a liquid-liquid-gas three phase separating tower, a process gas compressor, a decarbonizing tower, a temperature swing adsorption device, a propylene cooler, a liquefied gas separator, a liquefied gas product tank zone, an aromatization reactor, a pressure swing adsorption device, a methanol conversion device, a fuel gas pipe network, and an alkali liquor tank. Process flow of the method is short; operation is simple; materials are not recycled; influence on system load is low; and operation cost is low. 1400 to 2000kg of liquefied gas can be recycled per hour via the method, raw material resource is sufficient, a problem that too much liquefied gas is generated after methanol reaction is solved preferably, and a large amount of raw materials is provided for light dydrocarbon reactors.