Provided is a positioner for reinforcing steel bars of tunnel side wall. At least two groups of reinforcing steel bar positioning arm mechanisms are provided on the same side of an inverted trestle (4). The reinforcing steel bar positioning arm mechanism comprises a large arm (1), a medium arm (2) and a small arm (3). The large arm (1) is driven by a first telescopic cylinder (7) to rotate around a hinge point, such that the large arm (1) implements rotation in the horizontal direction. The medium arm (2) is composed of three second telescopic cylinders (8) in a Z-shaped arrangement in the vertical plane, such that the small arm (3) implements rotation or expansion in the vertical plane. Two arm rods of the small arm (3) are each provided with a third telescopic cylinder (9) to implement the expansion of the arm rod.