A quantum key distribution based optical network is a network formed by the interconnection of quantum key distribution devices through optical fibers. In the quantum key distribution optical networks, the key pool combines the characteristics of gradual accumulation and instantaneous consumption of secret keys to realize the efficient storage and management of key resources. This study analyzes the characteristics of quantum key distribution technology and the functional significance of the key pool. In addition, this study proposes a design of the “key as a service” framework and the quantum key distribution optical network architecture based on the key pool. A key pool construction method and a key resource scheduling method based on the architecture are proposed, and they are verified by a network simulation.