Using the theory of mental accounting in behavior economics, this paper divides the users' mental accounting when it participates in virtual community into 4 subaccounts concluding community attachment, knowledge sharing, maintenance of relationship and personal value recognition. By simulating the mental accounting of active persons and divers in virtual community to behaviors when they participate community topics, some conclusions of the users' numbers and influencing factors are drawn. These conclusions can help community operators grasp the deep-seated psychological needs hidden behind the users' behavior accurately. It has some significance in improving community management.