Drive motors in electric vehicles are mainly cooled by transmission fluid,which leads to large area contact between lubricating oil and electrical components containing copper or copper alloys.Therefore,it is of great practical significant to investigate the effect of base oil and additives in transmission fluid on copper corrosion.The effect of three different base oils and various additives in electric vehicle transmission fluid was evaluated by copper corrosion test under a long-time （168 h） and high temperature （150 ℃） situation.The corrosion of copper sheets was characterized and analyzed by inductively coupled plasma spectrometer （ICP）,scanning electron microscopy （SEM）,and energy dispersive spectrometry （EDS）.The corrosion mechanisms of four additives on copper sheets were explored.The results show that the base oil has a little effect on the copper corrosion performance,while the additives have a great effect on the copper corrosion performance,which is mainly affected by its type and chemical structure.Active chemical elements such as boron in dispersant,phosphorus/sulfur in antiwear additives are easy to cause corrosion on the surface of copper sheet under high temperature and longtime conditions.