A card substitution prevention method for a self-service terminal includes performing, by a card feeding portion of the self-service terminal, an alteration operation in the case that a card exists in a card reader of the self-service terminal, to make the card feeding portion unable to receive another card and prevent the another card from being placed in the card feeding portion. Also provided is a card substitution prevention apparatus for a self-service terminal. The method can effectively protect a card of a customer and prevent the card of the customer from being stealthily substituted, thereby improving service quality of a self-service terminal and maintaining trade credit of a merchant.