Abstract: Group buying is a new kind of dynamic pricing mechanisms on the Internet The mechanism makes the bidders as a group through Internet to get the volume discounts:the more bidders bid,the lower the auctioned object’s price becomes We analyze the strategy of bidders with IPV(Independent Private Value)model and build an incomplete information dynamic game model to illustrate the bidders’bidding process It is found that there exists a weakly dominant strategy If only discrete bid permitted,the strategy that a bidder bids the permitted price just no greater than his value is always weakly dominant,which means that the group buying auction is a kind of weakly incentive compatible mechanism.

Key words: bidding strategy, dynamic pricing mechanism, group buying, online auction