The invention discloses a method for reinforcing the strength of beam support concrete. The method comprises the following steps that an upper thrust anchor plate and a lower thrust anchor plate whichare provided with thrust grooves are fixedly mounted on a beam support, a right-triangle reinforcing area is formed by the upper thrust groove, the lower thrust groove and a joint of the beam support, and the included angle between the connecting line of the upper thrust groove and the lower thrust groove and a beam is 15-45 degrees; pre-bent channel steel is prepared, the wing edges of the two ends of the channel steel are cut off, pre-bent grooves are formed in the middles of the wing edges of the channel steel, the channel steel is pre-bent at a groove opening towards the groove opening, and two check anchor blocks are welded to the back face of the channel steel; the two ends of the pre-bent channel steel are mounted in the corresponding upper thrust groove and the corresponding lowerthrust groove, the pre-bent channel steel is tensioned upwards through a tensile rod arranged between the beam and the pre-bent channel steel until the check slopes of the two check anchor blocks arein full contact, the channel steel is fixed, and the pre-bent grooves are welded; and formworks are arranged on the two sides of the right-triangle reinforcing area and filled with the expansive concrete in a poured mode, after the concrete is hardened, the formworks are removed, and the check anchor blocks are cut off. According to the method, under the premise of basically not increasing the load of an original structure, the bending and shear resistance of the support can be greatly improved.