This paper analyzes the distribution of voltage and energy in a capacitor from the perspective of field and energy and the perspective of electric potential.In addition,it discusses the field intensity and energy issues when inserting a metal plate into the parallel-plate capacitor and changing the distance between the plates of the capacitor.The reasons why people are likely to make mistakes with respect to this are analyzed.It shows that people should get the hang of whether the capacitor and the power supply are connected and whether external force and the power do work.And the problems can be solved conveniently on the basis of energy conservation and a clear understanding of the energy change.