The present invention relates to a method of manufacturing an angled pipe with improved flexural rigidity. The purpose of the present invention is to reinforce a steel plate structurally by cold rolling and reinforcing ribs and save materials. The method of manufacturing an angled pipe with improved flexural rigidity according to the present invention includes a first step of preparing plate-shaped raw materials having uniform thickness; a second step of molding a reinforcement unit having a thinner thickness and a denser tissue than that in other sections by performing cold rolling on a portion of the raw materials prepared in the first step; and a third step of forming the plate-shaped material having the reinforcement unit and the reinforcing ribs by the second step into a quadrangle having four edges and four faces and manufacturing an angled pipe.
