The invention discloses a device for a bridge arm to form an equipotential body in a converter body. The device comprises the bridge arm, a first kind of short-circuit components and a second type of short-circuit components; the bridge arm comprises at least one valve tower, each valve tower comprises at least two valve tower layers, the neighboring valve tower layers in each valve tower are serially connected, each valve tower layer comprises at least two submodules, the neighboring submodules are serially connected, and each submodule comprises an outlet terminal and an inlet terminal; one short-circuit component of the first kind is arranged between the outlet terminal and the inlet terminal of one submodule, and one short-circuit component of the second kind is arranged between the inlet terminal and the outlet terminal of one valve tower layer.