For the electrostatic shielding effect,the electric field inside the metal shell is not affected by that outside the shell whether the metal shell is grounded or not.However,it cannot be obtained directly from Gauss theorem that the electric field outside the shell does not affect the electric field at any position inside the shell.In this paper,the electrostatic shielding effect is proved strictly by the uniqueness theorem of electrostatic field.In addition,the electrostatic shielding effect is further verified by numerical simulation.For ex...