Abstract: An olefin polymerization reactor capable of efficiently removing heat of reaction and having excellent energy saving properties is described. The olefin polymerization reactor includes a tubular powder container forming a moving bed in which powder moves downward by gravity, and including a plurality of intermediate openings provided spaced apart from each other in a vertical direction, a gas container that accommodates gas discharged from the plurality of intermediate openings, a powder feed pipe that feeds, to an upper portion of the tubular powder container, polyolefin powder and/or slurry containing polyolefin powder and olefin monomer liquid, a liquid feed pipe that feeds olefin monomer liquid to an inside of the tubular powder container, and a gas discharge pipe that discharges olefin monomer gas from the gas container to outside.

Abstract: Disclosed is a method for producing an olefin polymer by liquid phase polymerization, the method including a step of polymerizing an olefinic monomer system in the presence of a catalyst and a liquid medium in a polymerization reactor, wherein the reactor has an inner wall having an arithmetic average surface roughness of 1.0 ?m or less.