NOVELTY - Recycling ethylene in catalytic dry gas comprises cooling catalytic dry gas; removing methane and hydrogen in demethanizing column through rectification action and obtaining material stream enriched in ethylene on kettle of the demethanizing column; refrigerating through three-section compression using mixed gas comprising hydrogen, methane, ethylene, propylene and butane as refrigerant, and recycling cold energy.    USE - Method for recycling ethylene in catalytic dry gas.    ADVANTAGE - Recycling rate of ethylene is improved in large scale and the energy consumption is reduced. The method has less apparatus, simple flow, simple freezing circulation and less investment.    DETAILED DESCRIPTION - Recycling ethylene in catalytic dry gas comprises:    (A) after performing steps of removing acidic gas, drying and removing nitrogen oxides (NOx) and oxygen to catalytic dry gas from catalytic cracking device of refinery plant, introducing into a cooling tank to cool, after cooling, introducing into a heavy hydrocarbon separation tank, introducing the gas on tower top into cooling tank to further cool, sending the liquid on tank bottom to demethanizing column; after deeply cooling and throttling the gas on top of the heavy hydrocarbon separation tank, introducing into flash evaporation tank, after expanding the gas on top of the flash evaporation tank, introducing into cold tank to recycle the cold energy, and then discharging from the cold box, introducing the liquid on bottom of the flash evaporation tank into the demethanizing column;    (B) removing the methane and hydrogen in liquid entering into the demethanizing column through rectification action, introducing gas obtained from top of the demethanizing column into the cold tank to recycle cold energy, and then discharging from the cold tank, obtaining material stream enriched in ethylene on kettle of the demethanizing column; and    (C) introducing the mixed gas comprising hydrogen, methane, ethylene, propylene and butane into one-stage absorbing tank, two-stage compressing the gas of tank top, introducing the gas on top of the two-stage discharging tank into the cold tank to recycle cold energy, after cooling, introducing into a three-stage absorbing tank; after pressurizing the liquid on bottom of the two-stage discharging tank, introducing into the cold tank to discharge heat, after cooling, throttling through the throttle valve, and then returning to the cold tank to recycle cold energy, and then introducing into the one-stage absorbing tank; introducing gas on top of the three-stage absorbing tank into a third stage of compressor to compress, and then into cold tank to discharge heat, after cooling, introducing into a gas liquor separation tank; and then introducing the gas and liquid separated by the gas liquor separation tank into cold tank respectively, after throttling respectively, introducing into cold tank to recycle cold energy, and then mixing the gas with liquid, introducing into the one-stage absorbing tank, compressing again and again to refrigerate.