The present invention discloses a system and a method for recovering ethylene from high propylene light hydrocarbons or a methanol-to-propylene product gas. The system comprises a first deethanizer, a second deethanizer, a dryer, a hydrogenation reactor, a demethanizer, a demethanizer tail gas recovery unit and an ethylene rectification column, the demethanizer tail gas recovery unit comprises a combination absorber, an expander and a second gas-liquid separation tank; the upper section of the combination absorber is a deep-cooling rectification column section, the lower part of the combination absorber is an absorber section. A front-end deethanization front-end hydrogenation, twin-tower deethanization and intercooling C3-C6 light hydrocarbon mixture absorbs demethanizer tail gas, an absorbent is from bottom products of the first deethanizer and a depropanizer, and the second deethanizer and the ethylene rectification column are directly thermally coupled. The system can increase ethylene recovery rate of the apparatus, and reduces the loss of the absorbent to further reduce energy consumption and investment of the section of recovery of the ethylene from the product gas.