The invention relates to a protection box of an earth resistance tester, and belongs to the technical field of earth resistance testing devices. The protection box of the earth resistance tester comprises a box body used for containing a hollow shell of the tester, wire winding devices and an earth rod inserting groove fixedly formed in the back face of the box body, wherein the wire winding devices are arranged on the side faces of the box body and comprise wire winding wheels with a state of rotating around the axis to pay off and take up wires and a fixed state. According to the protection box, the wire winding devices are arranged, and therefore the problems that earth wires are disordered and prone to being wound in the earth resistance testing process are solved, the earth wires are easier and more convenient to pay off and take up, and the work efficiency is improved greatly. The functions of the wire winding wheels of the wire winding devices of the protection box are flexible and diversified, the wire winding wheels can freely rotate when paying off and taking up wires, the wire winding wheels are fixed when in a storage body shape and cooperate with wire press pieces, and the earth wires are wound in the wire winding wheels in order. The protection box is simple in structure, convenient to carry, high in testing efficiency, low in labor intensity, low in personnel requirement and good in comprehensive use performance.