China is the second-largest economy in the world yet it faces serious energy security challenges due to the country's reliance on coal, a fuel with multiple environmental and social problems. Moreover, since 2017 China has become the world's largest crude oil importer, greatly increasing its reliance on imported energy. The International Energy Agency has defined energy security as "the uninterrupted availability of energy sources at an affordable price," employing metrics in various dimensions such as availability, affordability, accessibility and acceptability to measure the energy security of different nations. Accordingly, the assessment, analysis and improvement of energy security is a complex problem. China's Energy Security aims to resolve this problem by answering three important questions:What are the difficulties and possibilities for China's energy security? How can we assess China's energy security in a qualitative or quantitative way? How can China's energy security be improved?