The invention relates to a low-temperature condensation separation method of a C2-C5 olefin tail gas. The method comprises the following steps: (1) adopting a heat exchanger for heat exchanging and cooling the C2-C5 olefin tail gas, and carrying out gas-liquid separation on the heat-exchanged and cooled gas through a first gas-liquid separator; (2) feeding obtained gas after separation into an expansion machine for expanding to low pressure, wherein the output work of the expansion machine is used for a generator set for generating electricity; (3) carrying out gas-liquid separation on the expanded gas through a second gas-liquid separator, carrying out heat exchange on the gas discharged from the second gas-liquid separator and the C2-C5 olefin tail gas in the heat exchanger, and discharging to reach standards; after pressurizing liquid olefin discharged by the first gas-liquid separator and the second gas-liquid separator, feeding into other technological processes so that the liquid olefin is used as a raw material for recycling. A system provided by the invention is particularly suitable for treating propylene in the tail gas, and is adopted for separating and extracting a propylene component, so that the hydrocarbon content in the tail gas is lower than a tail gas emission standard prescribed by the State.