The cyber-security classified protection system constitutes the fundamental cyber security regime in China. It aims to guarantee the security of national critical information infrastructure through graded protection of information systems. Water informatization systems integrate multiple technologies such as the Internet of Things, cloud computing and big data. Featuring uninterrupted continuous services, their business data security bears on national security, social order and public interest, hence imposing high requirements for cyber security. The classified protection system plays a vital role in security protection for water informatization systems.