Given that most commodity transportation depends on the maritime industry, the growing economy and increasing international trade volume are expected to accelerate the development of shipping activities and thus increase associated CO2 emissions. In order to identify the driving factors of CO2 emissions from China’s international shipping and find efficient mitigation strategies, this paper first estimates the CO2 emissions and presents the CO2 emissions features from 2000 to 2017. Second, the Logarithmic Mean Divisia Index (LMDI) method is applied to decompose the changes in CO2 emissions. Finally, the decoupling index is introduced to quantitatively examine the decoupling relationship between economic growth and CO2 emissions. The factors affecting the decoupling relationship are analyzed according to the LMDI results. The results indicate that CO2 emissions in maritime transport activities have experienced rapid growth during the study period. Economic growth appears to be the principal factor driving the CO2 emissions growth, whereas the overall effects of energy intensity and the commodity structure play a significant role in inhibiting CO2 emissions. The decoupling state over the study period has experienced four decoupling stages, with a distinct tendency towards weak decoupling. Economic activity has proven to be the most significant indicator influencing the decoupling relationship during the study period.