The invention discloses a grounding wire. The grounding wire comprises an upper copper bar and a lower copper bar, wherein the upper copper bar is connected with a grounding sleeve of a transformer shell; the lower copper bar is grounded; and a contact spike is arranged between the upper copper bar and the lower copper bar. Due to the setting of the contact spike, the used caliper type ampere meter can be selected from small-bore caliper type ampere meters. Therefore, the grounding wire has the characteristics of being free of a large-bayonet caliper type ampere meter when grounding current ismeasurement, and being convenient to carry and convenient to operate.