Before putting into operation,ultra-high voltage transformers need to undergo strict handover tests to ensure their safe and reliable operation. The grading capacity of the grading ring on the transformer will affect the accuracy of the handover test. When there are problems with high altitude environments or grading ring structures,their grading ability will change. It is particularly important to study and design grading rings that can have good grading ability in different situations. This article first uses COMSOL software to build a three-dimensional model of the withstand voltage test circuit of a 500 kV transformer. Secondly,the influence of changes in the pipe diameter and ring spacing of the equalizing ring on the equalizing capacity of the equalizing ring is studied. Finally,the variation of equalizing capacity of the equalizing ring in a rough state is studied. It is found that as the diameter of the equalizing pipe and the ring diameter increase or the distance between the rings decreases,the equalizing ability of the equalizing ring will be enhanced,with the greatest impact brought by the change in pipe diameter. When the grading ring has a rough surface,its grading ability will significantly decrease. Among them,the grading ability decreases most significantly when adhering to conical particles,and decreases least when concave,indicating that the smoother the surface of the grading ring,the better the grading ability. This study can provide some assistance for the design of grading rings for high altitude ultra-high voltage transformers.