Landfill gas separating and purifying process and device

The invention relates to a landfill gas separating and purifying process which comprises the following steps: separating landfill gas by adopting a methyldiethanolamine method; performing dehydration and pressure swing adsorption on a gas obtained by separation to obtain methane product gas; and performing flash evaporation and dehydration on a solution obtained by separation and then performing pressure swing adsorption to obtain carbon dioxide product gas. A landfill gas separating and purifying device comprises an absorption tower filled with methyldiethanolamine solution, a methane dehydrating device, a methane pressure swing adsorption device, a flash evaporation tower, a carbon dioxide dehydrating device and a carbon dioxide pressure swing adsorption device; a gas inlet of the absorption tower is connected with a raw material gas source, a gas outlet in the upper section of the absorption tower is sequentially connected with the methane dehydrating device and the methane pressure swing adsorption device; a solution outlet in the lower section of the absorption tower is sequentially connected with the flash evaporation tower, the carbon dioxide dehydrating device and the carbon dioxide pressure swing adsorption device. The process and the device disclosed by the invention can be used for simultaneously recovering carbon dioxide and methane from landfill gas, thereby reducing the emission of greenhouse gases and improving the purity of the gases.