Abstract-In this paper, we study the popular group-buying model in which theseller offers discount on the group-buying websites to attract new customers coming to experience its service. This paper analyses seller's pricing decision between only running offline business and joining the group-buying business. We find that when only running offline business, higher perceived service quality will bring more profit for the seller. However, if the seller joins the group-buying website and the perceived service quality is relatively low, seller's profit will decrease with it. If the seller's service quality is higher than the perceived service quality, he will improve his regular price after joining the group-buying website. Moreover, only when the group-buying website scale is relatively big can the seller make more profit by joining the group-buying website.