The utility model relates to a detachable electrode fixing device for testing alternating current impedance of concrete on site. The utility model belongs to the field of concrete detection instruments, specifically, the device comprises a connecting rod, pressure-bearing support arms are arranged at two ends of the connecting rod; the pressure-bearing support arm is fixed on the connecting rod through a knob; a pressure rod is arranged at the other end of the pressure-bearing support arm; a disc part is arranged at the end, penetrating through the pressure-bearing supporting arm and close toconcrete, of the pressure rod, an elastic component is arranged between the disc part and the pressure-bearing supporting arm and arranged on the pressure rod in a sleeving mode, a pulling part is arranged at the other end of the pressure rod, and a soft insulating material is arranged on the face, close to the concrete, of the disc part. The alternating-current impedance testing device is universally suitable for concrete columns, bearing beams and wall bodies with different thicknesses, plays a role in stabilizing alternating-current impedance testing, and is simple in structure and convenient to operate, and the cost is also reduced.