As one of the largest energy consumers and producers in the world, China has faced great challenge in energy security on the way of modernizing itself. Energy security mainly includes reliable energy provision and safe energy use. Reliable energy provision cares about whether a country's energy supply could meet its demand for population and economic development. Safe energy use tells us that we should reject the pattern of energy use at the cost of polluting environment. The paper analyzes the situation of China's energy security based on the analysis of energy resource base, balance between energy production and consumption, energy transportation and side effect of energy consumption. Owing to the pressure of economic development, China has placed much more emphasis on the security of energy provision than safe energy use, though it realized the importance of the latter in the past years. While it built its energy provision system, it polluted the environment greatly at the same time in such ways as lots of CO2 emissions, which contribute to the global warming, and the sinking of the earth's surface caused by coal mining. So it is time to rethink the goal of energy security. Energy security, as a determinant factor to the modern society, will become an increasingly sensitive issue in China when the country makes great strides in modernizing itself； and it could become even more sensitive in the next twenty to thirty years when China's population growth and economic development imposes more pressure on the national energy supply system continuingly. Based on the basic situation of China's energy security, this paper suggests that a new energy policy, including reliable energy provision and safe energy use, be needed for China's sustainable development in the future.