The present application is directed to a decoder, a coupling card reader and an application system. The decoder includes a card base which is produced from at least one type of materials selected from paper card, plastic card, metal thin card or organic glass thin card. The surface of the card base is applied with conducting coating. The conducting coating is provided with a plurality of conducting logic expression regions. Different conducting logic expression regions possess individual and independent conductive nature. The conductive nature of each conductive logic expression region on the conductive coating together form a sole conductive logic data coding for differentiating a specific decoder so that the decoder can be distinguished from other decoders. The present application is also directed to a card reader to be used with the decoder. The present application enhances the security level of data.