The invention discloses a method for separating low-carbon olefin gas. The method is used for overcoming the disadvantages in existing low-carbon olefin separation methods that cryogenic separation is complicated in process flow, large in investment and the like. The method comprises the following steps: the low-carbon olefin gas enters a deethanization tower after the low-carbon olefin gas is compressed and dried, a tower bottom material flow of the deethanization tower is conveyed to a depropanization and propylene distillation system so as to separate polymer-grade propylene products, and a tower top material flow of the deethanization tower enters a demethanization tower; and a tower bottom material flow of the demethanization tower is conveyed to an acetylene converter and an ethylene distillation tower, a tower top material flow of the demethanization tower is conveyed to an absorption tower and is in contact with an absorbent, a tower top gaseous-phase material flow of the absorption tower is output or enters a fuel gas system, and a tower bottom material flow of the absorption tower is conveyed to the deethanization tower. The method disclosed by the invention has the advantage that the cryogenic separation is simple in process flow and small in investment and can be used for producing target products, such as polymer-grade ethylene, polymer-grade propylene and the like.