Abstract: From the perspective of Helmholtz＇s theorem, the inherent relationship between electric displacement vector and the source is made clear, and that the electric displacement vector is relevant to dielectric, polarization charge and the boundary conditions as well as the distribution of free charge is pointed out, putting emphasis on the prerequisites for interaction between electric displacement vector and the distribution of free charge.

Key words: Helmholtz＇s theorem, electric displacement vector, free charge