The invention discloses a method, a device and a system for measuring a high-voltage AC transmission line voltage grade. The method comprises steps: a function model among the high-voltage AC transmission line voltage grade, a vertical projection distance between a sampling point and the high-voltage AC transmission line and the electric field intensity at the sampling point is built; an inverse function about the high-voltage AC transmission line voltage grade and the vertical projection distance between the sampling point and the high-voltage AC transmission line is acquired; the electric field intensities of any two measurement points in the high-voltage AC transmission line and the displacement components of the two measurement points in the vertical direction of the high-voltage AC transmission line are acquired; and according to the electric field intensities, the displacement components and the inverse function, the voltage grade of the high-voltage AC transmission line is calculated and obtained. The high-voltage AC transmission line voltage can be detected in a non-contact and remote mode.