To produce an olefin in a high purity and at a low cost from a decomposed gas under a mild condition by compressing, washing and performing a selective hydrogenation of a decomposed gas, then scrubbing and olefin stripping the gas, and then separate-treating a gas flow rich in olefin therefrom.

This method for chemical absorption for recovering olefins from a decomposed gas comprises compressing the decomposed gas by 50-250 psi pressure to obtain a compressed and decomposed gas flow, washing the gas to remove an acidic gas, performing a selective hydrogenation of acetylene and dienes contained therein, treating the hydrogenated, washed and compressed gas flow by a scrubbing solution containing a metal salt in an absorbing agent column to obtain a scrubbed liquid state flow rich in olefins, treating the flow in an olefin stripper to obtain a stripped gas flow rich in olefins, and then separating the gas flow into a product flow rich in ethylene, a product flow rich in propylene and a product flow rich in 4C olefins.