Abstract: With the intensification of human activities and the sustainable development of the social economy, the exploitation of islands has intensified. Dynamic evaluation of the ecological security status in the development of island is a prerequisite for proposing ecological environmental protection measures. In-depth analysis of the main factors affecting island ecological security is an objective basis for accurately adjusting island development policies. It is of great significance to alleviate the contradiction between island development and ecological security and realize the coordination between island construction and ecological environment. Based on the case in Pingtan Island, this study screened 34 evaluation factors to construct an ecological safety evaluation index system. The indexes cover social, economic and environmental aspects. Using entropy weight method to calculate the weight of each evaluation index improves the objectivity and accuracy of the evaluation. Based on entropy weight method, the ecological security of Pingtan Island from 2005 to 2015 was evaluated dynamically by principal component projection method, and the objectivity and accuracy of the evaluation were improved. It is found that the worst and the best years of ecological security situation were 2006 and 2011, respectively. The ecological security projection value in 2006 was the smallest and it was only 0.004 1. The highest ecological security projection value in 2011 was 0.178 1. Based on the map of ecological security situation, it is found that the ecological security projection value in 2009 and 2011 changed obviously. The driving force analysis showed that 9 social and economic indicators, including the total retail sales of social consumer goods growth rate, financial expenditure, fixed asset investment growth rate, industrial growth rate, tourist number, unemployment rate, total output of aquatic products, garbage harmless treatment rate, average annual loss rate of cultivated land, of ecological security situation of Pingtan Island play important influence with the grey correlation method.