Coastal areas have the most obvious ocean–land interaction and experience the most frequent human activities. As the development of coastal areas has a high degree of spatiotemporal variability, local governments bear direct responsibility for marine governance, yet accurately evaluating and analyzing local governments’ marine governance efficiency in coastal areas is challenging. This study constructs a spatiotemporal coupling coordination model to comprehensively evaluate local governments’ marine governance efficiency in six coastal cities in Liaoning Province from 2004 to 2019. A complex system was necessary to obtain the development level, discrete degree, and development speed of each subsystem. The construction of the evaluation index system was the foundation, and the construction of the spatiotemporal weight matrix was the key. The results show that overall, the local governments’ marine governance efficiency level is generally increasing, and the agglomeration effect is obvious. The efficiency of each cities’ economic, ecological, and social governance subsystem is in a process of continuous and dynamic change. The coupling and coordination degrees of the six governance systems have continuously improved and the spatial and temporal differences have decreased; each city shows different coupling and coordination degrees in each subsystem. Regarding the factors affecting comprehensive marine management, Liaoning’s coastal areas fail to attract foreign tourists; the discharge and treatment of industrial wastewater restricts ecological governance; and the reduction of fisheries hinders the social governance system’s efficiency. The results contribute to the understanding of costal cities’ marine governance and promote the sustainable development of coastal areas.