Coastal Ocean Prediction System (COPS), its structure (subsystems), function and optimization, is described in this paper based on existing European COPS. An COPS consists four subsystems, i.e., external forcing system, ocean observing system, ocean modeling system and data dissemination system. The best quality of marine environmental service can only be reached by optimizing the four subsystems together rather tan a single system. Key issues in COPS optimization, such as ensemble prediction by using different Met-Ocean models' forecasts, cost-efficient ocean observing system design, improving COPS predictability, technology chanllenges in COPS, role of virtual center in integrating the national activities and avoid the redundency, are discussed in details.