Currently, China has become one of the biggest energy consumers and importers in the world, and its energy policies will increasingly affect international energy situation. This paper introduces a new aggregated indicator, the China energy security index (CESI), for evaluating how China's energy security has changed over years. The CESI includes the energy supply dimension, economic-technical dimension, and environmental dimension of energy security. Based on the banding approach, 18 indicators, which are selected from six years 1990, 1995, 2000, 2005, 2010, and 2014, are normalized to form the CESI and sub-indexes. As to the energy supply dimension, the indigenous energy availability sub-index and energy dependence sub-index continued decline over the study period. Among all the three dimensions of CESI, the largest changes observed are in the energy supply sub-index. The change of CESI likes a 'N' curve. In this study, China's worst energy security performance was in 2010 and the best was in 2000. At last, the SWOT analysis method is utilized to deprive China's energy security policy implications.