In this paper, we establish a simple repetition game model to study the value of seller's reputation in online auction. Using the stamp data colleted from Taobao and eBay, the article also empirically investigates the impact of seller's feedback score on the product's transaction probability and final price, respectively. The results suggest that it is worthwhile building a good reputation in online auction for a seller because of the significant increase of the item's transaction probability. However, the feedback score has little effect on the final transaction price of the product.