Abstract: Based on information sharing influence on consumer activities, the paper studies how consumers group buying behavior changes and who dominated, which are difficult points in the process of group behavior research. In the online purchasing system, time and resource are limited, and both sides in business have marginal effect with the increase of negotiation time. When new consumers join in the network, other consumers will shorten the negotiation time. Meanwhile, new consumers without group purchase experience will shorten the negotiation time, and quickly join in the group activities.

Key words: buying alliance, information sharing, consumer surplus