In MANETs, most network functions count on node cooperation. Forwarding packets of other nodes is a basic example of such cooperation. However, nodes may not be interested in forwarding the requested packets because of being selfishness or malice, which significantly degrades network performance. Therefore, in respect of node forwarding process, we propose a global punishment-based repeated-game model and investigate the equilibrium conditions of packet forwarding strategies when the whole network is in a cooperative state. This model takes node rationales into consideration. Moreover, in order to reduce the selfish nodes’ future payoff to stimulate cooperation, metamodel is utilized to design forwarding strategies. Simulation results show that the proposed game model with punishment mechanism can promote node forwarding probability.