Studies in vehicular ad hoc networks using public goods game theory to enhance the cooperation show that the performance of cooperation in those types of network would have been poor in the areas with high vehicle density. In this paper, the result of simulation shows that the certain range of degrees of vehicle will enhance the cooperation in network. Therefore, we propose a grouping game model with the concept of the game degree and game topology to enhance the cooperation in the areas with high vehicle density. This model can change the game topology and reduce the game degree of nodes. The experimental results show that using this model in any high density regions of vehicles can significantly enhance the performance of cooperation in the network.