To provide a method for producing an ethylene--olefin-based copolymer by continuous multi-stage polymerization, by which the ethylene--olefin-based copolymer excellent in a balance between strength and elongation is obtained.

This method for producing the ethylene--olefin-based copolymer, comprising continuously polymerizing ethylene with an -olefin in the presence of an olefin polymerization catalyst in a solvent in a polymerization reaction device in which two or more polymerization tanks are connected to each other in series, is characterized by having the first polymerization process for producing a polymer component in a polymerization condition in which a flow state is 1.5 tanks as a perfect mixing tank line model, and the second polymerization process for producing a polymer component in one polymerization reaction device in a polymerization condition in which a flow state is 1.5 tanks as a perfect mixing tank line model, and the (n1/n2) ratio of the tank number (n1) in the perfect mixing tank line model in the first polymerization process/the tank number (n2) in the perfect mixing tank line model in the second polymerization process is 1.5.