With the development of smart grids and the energy Internet, large-scale monitoring of voltage and electric field data is required in all aspects of power systems, which requires the arrangement of various advanced sensors. Measurement of the electric field can replace traditional voltage transformers to realize the non-contact measurement of voltage, which reduces the insulation cost and the difficulty of operation and maintenance. Electric field measurement can also be applied in various other areas, such as equipment fault diagnosis, lightning warning, and electromagnetic environment measurement. Traditional electric field measurement devices, such as field mills, are bulky and costly, so they cannot be arranged flexibly on a large scale. In this paper, we present an electrostatically actuated micro-electric field sensor (E-sensor) with a piezoresistive sensing structure. The presented E-sensor is fabricated into a four-cantilever structure using microfabrication technology. The cantilevers are displaced under the drive of the electrostatic force, and the generated strain is transformed into measurable signals through piezoresistive materials. The presented E-sensor has the advantages of small size, low cost, low power consumption, and easy mass production. Moreover, the E-sensor has a high signal-to-noise ratio, high resolution, and wide measuring range. The experimental results show that the E-sensor has a linear electric field measurement range from 1.1 to 1100 kV·m⁻¹ with an alternating current (AC) resolution of up to 112 V·m⁻¹·Hz^−1/2 and a cut-off frequency of 496 Hz, making it suitable for most applications in smart grids and the energy Internet.