Abstract: This research topic came from the contradiction between the rapid growth of online shopping transactions and the scant understanding on the charging mechanism of the Internet trading platform. The question need to be answered is that where does the Internet trading platform gain profit from, and how can they improve the profit. By establishing a tripartite game model, the relationship between the Internet trading platform, manufacturers and consumers is analyzed, how the decision from a part affect the decision from another part is explained. The results show that the Internet trading platform gains from the auction of advertising seats and the charge of the seat are positive correlated with the cost on dealing with information of good by consumers. By using simulated data, the model provides explains for the following facts: First, clothing merchandise gradually replace book commodities in online shopping market.Moreover, as consumers are willing to purchase more expensive goods on the Internet, the cooperation between the trading platform and manufacturers become more stable, goods with higher information costs were squeezed out of the market. Therefore, the consumer purchases brand goods instead of non-branded goods gradually online.This study could help government, consumer and company to make their decision. The research of Internet trading platform can also profoundly promote Information economics.

Key words: Internet trading platform, charging mechanism, advertising seats, tripartite game model