Controllable adhesion different from permanent sticky connection, can achieve repeatable attachment and detachment to surfaces of nonconductive substrates, and obtain extensive attractions and applications in climbing robots, silicon-based electronics, clinic treatments, etc. Whereas the electrostatic adhesion technique offers controllable adhesions by switching power, the adhesion strength is much weaker than permanent glue and tapes. We derive electrostatic adhesion strength expression according to the Maxwell stress tensor method and develop the effective width model to optimize adhesion strength. By combining dimensional parameters of electrode rings into a single variable, we pinpoint the optimum condition with one defined parameter of effective width, leading to predictions of the maximum limit of adhesion. We reveal the importance of optimizing the dimensional parameters of electrode rings, not only applied voltages and air gaps. Although the effect of thickness of substrates was typically ignored, it rarely affects adhesion analysis only when substrates are thicker enough. Electrostatic adhesion pads with various electrode ring numbers were fabricated and assembled. Experiment results and reference data supported this strength optimization strategy. We also designed a soft robot based on our optimized electrostatic adhesion pad and origami pneumatic muscle. It moves in an inchworm pattern, and it is highly impact-resistant due to the soft materials.