Abstract: The factors influencing an emission-reduction-decision of ports and shipping companies are analyzed from the angle of supply train. Two decision-making game models are built based on the game theory, for centralized and decentralize decision-making respectively. The two models lead to different emission-reduction strategies. The comparison between them show that centralized decision ensures the best port-ship overall profit objective. The difference of emission-reduction cost for with and without port’s cooperation decides the final decision. It is also seen that introduction of carbon tax and the environmental awareness of clients are effective driving forces to put emission-reduction into practice.