The next-generation wireless network is envisioned as a convergence of different wireless access technologies, and can offer mobile users the best service anywhere anytime. While mobile users roam between heterogeneous access networks, vertical handoff may take place and vertical handoff decision (network selection) would be a clear challenge. Because game theory is an effective mathematical theory to deal with models for studying interaction among decision makers, in this paper, the competition between mobile users and heterogeneous access networks can be formulated as a multi-tenderee bidding model; at the same time, the competition among heterogeneous access networks can be formulated as a cooperative game process to seek for larger total payoff. Then, the proposed algorithm is evaluated by network utility and standard deviation through simulation, and the experimental results show that it is effective to achieve the load balancing and meet the quality of service (QoS) requirements of various applications.