Abstract: Artificial reef forms one of the most important marine ecosystems. Understanding its energy flows and trophic structure is of fundamental importance to the ecological restoration and ecosystem conservation. Based on the investigated data in the artificial reef in Juehua island in the spring, summer, and autumn of 2019, a mass-balance model for the artificial reef ecosystem was constructed by joining the stable carbon and nitrogen isotopes and the Ecopath model to explore its energy transfer and functions. We found that the energy flows were dominated by the primary producer. The trophic levels of the functional groups ranged from 1.00 to 4.10. Platycephalus indicus (Linnaeus) had the highest trophic level. Charybdis japonica was the keystones species of the food web.The total energy transfer efficiency of the system was 6.28%, indicating that the energy utilization is not sufficient. The ratio of total primary productivity to total respiration of the system was 2.98, indicating that the system is in autotrophic succession. The connectivity index and system omnivory index were 0.28 and 0.32, respectively. The Finn's cycling index and the mean path length of the energy flow were 6.08% and 2.49, respectively. The ecosystem's scale, current Finn's cycling level, complexity and stability of the ecosystem implied the system at a high level in the system of adjacent regions. The ecosystem is in the development stage, and there is still a gap from the mature ecosystem.