To thoroughly investigate the feasibility of carbon fiber anchor cable support in coastal deep excavations, a field test was conducted on cast-in-place pile+prestressed carbon fiber anchor cable support based on a deep excavation project in Yantai City. This study analyzed the prestress loss laws and deformation patterns of the deep foundation pit during excavation under the action of prestressed carbon fiber anchor cables using a complete set of construction techniques. The study results show that the prestressed carbon fiber anchor cable has been successfully applied in coastal deep foundation pit support projects.