The influence maximization on single network has aroused widespread concerns and has become a research hotspot. However, there is a trend of information exchange between multi-social networks. The bridge user (BU), which refers to the user that has multi-accounts on multi-social networks, has the ability to share the information from one social network to another. Due to this, information spread is not limited to a single network. In this paper, we study the influence maximization on multi-social networks. We analyze the role of bridge user in multi-social networks information spread and propose a multi-social network aggregation algorithm based on bridge users, then we solve the problem of influence maximization on multi-social networks based on aggregate graph. Experiments solve the problem of influence maximization on multi-social networks and confirm the role of bridge users in the information spread on multi-social networks.