Energy is an essential material foundation for ensuring economic sustainability and national security. With the development of digitalization, the importance of digital finance in promoting the green and low-carbon transformation of the economy has emerged. The ocean is a national energy treasure house. In order to explore whether digital finance improves the carbon emission efficiency of marine energy, this paper selects panel data from 11 coastal areas from 2011 to 2019 in China and uses the panel fixed effect model, mediation, and moderation model to analyze the mechanism between them empirically. The results show that: (1) digital finance improves marine energy carbon emission efficiency, and the depth of use has the most obvious effect; (2) the incentive effect is heterogeneous due to different geographical locations, resource endowment degree, and digitalization degree; (3) the marine energy consumption structure plays a mediating effect, and marine industrial structure and technological innovation can enhance the impact of the digital finance on marine energy carbon emission efficiency. Therefore, optimizing the energy consumption structure and giving full play to the effect of digital finance in promoting the efficiency of marine energy carbon emission to help accelerate the low-carbon development of China's economy and the realization of carbon emission reduction.