To ensure water security, the Chinese government started to desalinate seawater early, rolling out policies on seawater desalination, with them ranging from science and technology to the industrialization of seawater desalination. And desalinated seawater is moving into a unified allocation of water resources. In this paper the evolution of policies on seawater desalination was analyzed and the seawater desalination policies attached to water security policies were emphasized. Meanwhile, the content analysis method was used. The characteristics of the evolution of policies can be as follows: First, the Ministry of Industry and Information Technology has continually become one of the main policy-making departments; second, changes are not continuous and demand-side policy tools account for the least; third, the policy tools provided by the water security policies basically show a downward trend. Although Chinese government has made progress in seawater desalination policies, there are still challenges for further development such as imperfect policy system, proportion of multi-sectoral policies, the combination of policy tools, and unsatisfactory condition policy tools provided by the water security policies. Finally, recommendations were proposed in the paper, including to accelerate the promulgation of laws and regulations, to pay more attention to joint policies, to strengthen talent training and special technical support, as well as to stimulate the development of demand-side policy tools and leverage the role of water security policies.