The power transformer is a critical and indispensable component of the power system, playing a pivotal role in the transmission network and ensuring the reliable operation of the power transmission system. The reliability of its operation is directly related to the safety and stability of the power system. Once these devices fail, the consequences are very serious. Insulation faults prevail among issues affecting power transformers, with partial discharge serving as a significant symptom and manifestation of these faults, particularly interturn discharge which accounts for more than half of such occurrences. For this reason, the early fault characteristics and development rules of winding discharge under normal and overheating oil temperature conditions are investigated based on the trend of multi-parameter variation. This study provides a theoretical basis for establishing early fault characteristics criteria of interturn discharge.