The invention discloses a drilling jig for isometric balance holes of a brake drum, and solves the problems of complex adjustment and assembly and disassembly processes of the conventional jig and large interval errors of drilled holes. The drilling jig comprises an L-shaped bracket (1), a roller hanging drum (2) and the brake drum, wherein the upper end part of the other side face of a vertical plate of the L-shaped bracket is movably provided with a T-shaped longitudinal stroke block (3) with a longitudinal guide slot (14); the top plate of the T-shaped longitudinal stroke block (3) is fixedly provided with a transverse stroke block (10) in the horizontal direction; one end of the transverse stroke block (10) is provided with a transverse guide slot (12), and the other end of the transverse stroke block (10) is provided with a drilling guide block (9); the drilling guide block (9) is arranged above the brake drum and provided with a drill passing hole (13) of a radial drill; and left and right sides of the drill passing hole (13) are provided with a pin axle hole (8) respectively. The drilling jig has the advantages of simple operation and convenient replacement and maintenance.