Method for producing olefin polymer

Provided is a method for producing an olefin polymer in which an olefin polymer is obtained by polymerizing an olefin compound at a temperature of 0 DEG C or less under the presence of a Lewis acid catalyst, said method comprising: a supply step in which a raw material liquid comprising an olefin compound is supplied into a reactor that is provided with a cooling means; a polymerization step in which the olefin compound is polymerized within the reactor and a reaction liquid comprising an olefin polymer is obtained; a deactivation step in which a deactivator is added to the reaction liquid that has been removed from the reactor and the Lewis acid catalyst is deactivated; and a cold energy recovery step in which the reaction liquid that has been subjected to the deactivation step is supplied to a cold energy recovery means and cold energy is recovered from the reaction liquid. The amount of the Lewis acid catalyst with respect to the total amount of the olefin compound is 0.5 * 10-3 to 1.0 * 10-1 mol%. 种制造方法，其