Charge is a fundamental physical property of matter that is responsible for its interactions with electromagnetic fields. The real nature and the essence of charge are unknown. In this paper, a new theory is presented to describe the nature and the essence of electric charge is formulated based on the vortex model of the electron which has a finite size and has an irrotational vortex structure. This theory and the vortex model of the electron enables us, for the first time, to describe the origin of bivalency, stability, quantization, equality of the absolute values of the bivalent charges, to derive a simple formulation to calculate the electric charge based on hydrodynamics without the use any constant. The difference between negative and positive charge, is revealed and the charged particles interactions are described. The electric charge is an expression of accelerated spherical mass per area reduced by the stiffness of the vacuum which has the units ε 0 ML 3 /T 2 . The calculated results based on these equations comply accurately with the experimental results.