The online chat group is a small-scale multiuser social networking platform, in which users participate in the discussions and send and receive information. Online chat group service providers are concerned about the number of active members because more active members means more advertising revenues. For the group owners and members, efficiency of information acquisition is the concern. So it is of great value to model these two indicators' impacting factors. This paper deduces the mathematical models of the number of active members and efficiency of information acquisition and then conducts numerical experiment. The experimental results provide evidences about how to improve the number of active members and efficiency of information acquisition.