Vortex electric field (VEF) is one of the difficulties in the course of “Electromagnetics”. Although the loop integration and curl can accurately describe its differences from the electro-static fields (ESF), the unglamorous mathematical formulas cannot help students to understand their physical essence. Walter Lewins demonstration experiment on voltage measurement in a VEF intuitively presents the difference between VEF and ESF, but it also brings many doubts to students. This article discusses the distribution of electric field and charge accumulation in a conductor circuit in a VEF under equilibrium, and answers the question of what the “voltage” measured in a VEF is. These analyses are beneficial for deepening students understanding of the concept of VEF and its differences from ESF, while it also cultivates the scientific spirit of seeking the essence through phenomena.