Towards the safety operation of composite insulators, research was conducted for the nondestructive detection of debonding defects in composite insulator using the method of the adjacent capacitance. The feasibility of adjacent capacitive sensing technique for the detection of debonding defects in multilayer dielectric structures and the effect of electrode width and spacing on the detection capability of adjacent capacitive sensors were investigated through numerical simulations and experiments. It is demonstrated that the adjacent capacitive sensing technique can be used for the detection of debonding defects at the interface of multilayer dielectric structures, and the electrode width and electrode spacing have an effect on its detection performance. The detection efficiency and resolution of the adjacent capacitance detection technique can be improved by optimizing the electrode parameters. The research provides a feasible technical solution for debonding detection in composite insulator.