Current underwater monitoring systems suffer from lack of unified development criteria, low software reusability, resulting in that it is hard to design and implement system fast and efficiently. This paper presents a design method of monitoring system based on underwater sensor networks. Monitoring data model is formed by standardizing the monitoring metadata and monitoring data. Scalable functional component library is constructed and can be quickly configured to generate systems that meet user demands. Through the validation in different application developments, this method is proved to improve the development efficiency and guarantee system quality.