NOVELTY - Fluid catalytic cracking dry gas is provided into a refinery catalytic cracking device, pressurized through primary pressure swing adsorption tower to separate into ethylene-rich dry gas and concentrated gas. The concentrated gas is separated into hydrogen gas and desorbed gas. Portion or total of desorbed gas and ethylene-rich dry gas are mixed, to form ethylene-rich mixed dry gas. The resultant product is separated into permeate gas and non-permeate gas. The non-permeate gas is separated into ethane, ethylene, propylene and methane-rich combustion gas by a cryogenic separation system.    USE - Separation and purification of fluid catalytic cracking dry gas (claimed).    ADVANTAGE - The method enables separation and purification of fluid catalytic cracking dry gas with high yield, and provides clear and high-purity fluid catalytic cracking dry gas. The method improves yield and purity of each gas component of dry gas.    DETAILED DESCRIPTION - Fluid catalytic cracking dry gas is provided into a refinery catalytic cracking device to increase pressure to 0.7-1.2 MPa, pressurized through primary pressure swing adsorption tower to separate into ethylene-rich dry gas and concentrated gas, in which ethylene-rich dry gas is desorbed in primary pressure swing adsorption tower. The concentrated gas is entered into a secondary pressure swing adsorption tower, and separated into hydrogen gas and desorbed gas. Portion or total of desorbed gas and ethylene-rich dry gas are mixed, and pressurized to 1-3.5 MPa, to form ethylene-rich mixed dry gas. The resultant product is subjected to membrane separation process to separate into permeate gas and non-permeate gas. The permeate gas is provided into primary pressure swing adsorption tower. The non-permeate gas is separated into ethane, ethylene, propylene and methane-rich combustion gas by a cryogenic separation system. The main component of ethylene-rich dry gas is carbon two-component gas including olefin gas including two or more carbon atoms. The main component of concentrated gas is hydrogen, methane and nitrogen. An INDEPENDENT CLAIM is included for device for separation and purification of fluid catalytic cracking dry gas, which has a primary compressor, a secondary compressor, primary pressure swing adsorption tower, secondary pressure swing adsorption tower, membrane separation device and cryogenic separation system. The output terminal of the primary compressor is connected to bottom inlet of primary pressure swing adsorption tower. The bottom outlets of primary pressure swing adsorption tower and secondary pressure swing adsorption tower are connected to input terminal of secondary compressor. The output terminal of secondary compressor is connected to feed side of the membrane separation device. Permeate side of the membrane separation device further connected to bottom of primary pressure swing adsorption tower. The non-permeate side of membrane separation device is connected to cryogenic separation system.