Energy has played an important role in development of economy and society, security of which has become a focusing issue. Firstly, the authors have put forward a definition of regional energy security and have explained its interacting system elements in the light of the system theory and existing energy security research literatures. Secondly, the authors have established a set of index system, which consists of 10 composite index and concerns energy-economics, energy-environment, energy-population subsystem and introduced the algorithm of principal component analysis. Finally, according to the statistical data of Jiangsu province and by virtue of principal component analysis, the authors have analyzed the energy security status of Jiangsu province and have revealed its declining trend during the 1990-2007 under the current energy policy and socio-economic conditions. The result is in accordance with the actual situation of Jiangsu provincial energy system, which indicates that the established composite index system and used principal component analysis are effective in evaluating the regional energy security condition, the method can disclose the existing obstacles in the process of energy security system operation and provide a decision-making basis in guaranteeing the regional energy security.