The micro-EDM in nitrogen plasma jet (NPJ) obtained better processing performance than that in gas. However, due to the small discharge gap and the difficult exfoliation of the molten material, the abnormal discharge phenomena such as short circuit and arcing still occurred frequently. These phenomena seriously affected the quality and stability of the processing. In this paper, a new method of applying ultrasonic vibration to the workpiece is proposed to improve the processing performance of micro-EDM in NPJ. The process experiments were carried out on process indexes such as discharge distance, material removal rate (MRR), surface roughness and tool electrode relative wear rate (TWR) of EDM. The experimental results show that after the ultrasonic vibration is applied to the workpiece, the molten material is more easily exfoliated from the surface of the workpiece. When the mixture of nitrogen plasma jet and high velocity air jet (NPJ+HVAJ) is used as the dielectric in the proposed method, the MRR increased by 13%, the surface roughness decreased by 19%, and the TWR decreased by 13%.