The utility model provides a partial-discharge-free inflatable grading ring for an extra-high voltage field test and an installation method thereof. The grading ring comprises an oval annular inflatable inner container and a conductive shielding flame-retardant layer attached to the outer surface of the inflatable inner container. The conductive shielding flame-retardant layer is made of self-adhesive aluminum foil glass fiber cloth with clear glass fibers on the surface; the rated inflation pressure of the inner container is 0.2 MPa, the 24-hour pressure drop of the inner container under therated inflation pressure is smaller than 3%, the conductive shielding flame-retardant layer surrounds the outer surface of the inner container by a circle from one side of the inner container to wrapthe inner container, and an opening area with the width ranging from 12 mm to 18 mm is reserved outside the inner container. The device is simple in structure and convenient to install, can greatly improve the working efficiency of a field high-voltage test, reduces the labor intensity of a tester, and improves the reliability level of a power system.