Abstract: A system and method for promoting product sales are proposed and applicable to data processing devices, characterized in the use of a computing mechanism for calculating the unit profit of a main product according to sales-related information of the main product and a promotional product thereof; a judging mechanism for judging the appropriateness of the promotional content so as to come up with a reasonable scheme for the product promotion, and further provides related information of the promotional schemes for reference and selection. In addition, the sales-promoting system and method of the present invention further provides inquiry and checking of the promotional scheme.