Abstract: The transformer oil oxidation stability was tested by two methods of classical NB/SH/T 0811 and ASTM D2112 Rotating Bomb Oxidation, different results were observed. The inconsistency is caused by high temperature (140℃) and lower oxygen pressure (620KPa) of the RBOT method. At the optimized conditions of 120℃ and 1500KPa, and taking the time at which the quick reduction of oxygen pressure occurs as the end point, the consistency of the two methods is obtained. Based on these experiments, an easy and reliable method as early assisted method for evaluating oxidation stability of transformer oil is established with best resolving power and repeatability.