The invention relates to a transaction data processing method and system based on discount coupon information. The method comprises the following steps: enabling a POS terminal to obtain discount coupon information; enabling the POS terminal to transmit the obtained discount coupon information and transaction information to a discount vertical reduction platform, wherein the transaction information comprises card information, merchant information and an original transaction amount; carrying out the discount confirmation: enabling the discount vertical reduction platform to judge whether thereis a discount coupon or not based on the discount coupon information: returning discount transaction information to the POS terminal if there is the discount coupon, or else ending the transaction, wherein the discount transaction information comprises the original transaction amount, a discount deduction amount and an actual transaction amount; enabling the POS terminal to transmit the card information, the merchant information and the actual transaction amount after deduction to an acquirer, and then to be transferred to a bank card background system for the processing of the transaction. According to the invention, the method can achieve the instant obtaining of the deduction discount of the transaction amount during transaction, and can enable a card holder to have good transaction experience.