Due to the absence of centralized authority, the service reliability of wireless ad hoc network is seriously affected by selfish actions of the rational nodes during the packet forwarding. This paper proposes a repeated-game model of node behavior that takes account of the selfish nodes' future payoff expectations and their long-term desires for profit. An incentive-compatible condition under which the selfish one will be deterred from cheating by the subsequent punishments and then turn to cooperate is shown analytically. The impacts on the selfish nodes' behaviors, which are induced by their willingness for future collaboration, the parameter settings of punishment mechanism and the efficiency of misbehavior detection, are also discussed. Simulation results show that, the increase of network scale, the deterioration of node's collaborative patience and the low misbehavior detection efficiency will motivate entities toward self-interested action, but this tendency can be neutralized by a careful configuration of the punishment mechanism in the model.