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Capacitive Power Transfer (CPT) technology has been proposed and investigated recently as an alternative contactless power transfer method which has the advantages of being able to transfer power across metal barriers and causing low power losses in metal surrounding circumstances. However, more fundamental researches are needed to guide CPT coupling analysis and design. Based on the Duality Principle, this paper proposes a generalized coupling model to describe the electric field coupling between the primary and secondary side of CPT systems. The concept of mutual capacitance is extended in a CPT system to decouple the primary and secondary circuits. A new term capacitive coupling factor is introduced to provide a direct comparison for different coupling design. The coupling model for multiple pickups is also developed. A CPT prototype has been built and the experimental results have shown that the new model can be used to improve the circuit tuning for significant output power increase.