The invention discloses a de-emulsifying agent and a method for preparing the same. The de-emulsifying agent is a polyether compound prepared by alkoxylation reaction of poly (amidoamine) (PAMAM) and epoxy compounds. The invention adopts the PAMAM with a dendritic multi-branch structure as an initiator for synthesis the de-emulsifying agent. The obtained de-emulsifying agent has the characteristics of a plurality of branched and large molecular weight. The de-emulsifying agent has good interfacial activity, infiltrability, good crude oil emulsion de-emulsifying performance, and wide applications in crude oil exploration, oil refining and other fields.