As the main component of international transportation, the shipping industry cannot be underestimated in pollutant emissions. To control the emission of pollutants, IMO and the major countries have designed ECA to limit ships’ emission in the offshore area. The implementation of ECA has a direct impact on the ship’s cost. Therefore, this paper studied how the ship’s behavior changes under ECA policy. Furthermore, we simulated the ship’s evasion trajectory under different ECA policies using AIS data. Meantime, the change of ship cost and emission reduction under different policies is analyzed. We found that the distorted emission reduction is increasing first and decreasing with the ECA boundary moving far away from the coastline. The saved cost by evasion behavior has the same variation trend. Furthermore, the emission reduction efficiency related to the increase in ship’s operating cost has a peak value with the distance of ECA boundary moving. This study could help the government to evaluate and design ECA policy.