## 1 Introduction  
Life expectancy, one of the most important indices in evaluating human health and aging, could be regarded as a comprehensive index reflecting levels of development in regional economy, education and healthcare [1]. To improve human wellbeing and ensure healthier living conditions, the United Nations' Sustainable Development Goals (2015-2030) explicitly advocated reducing global pregnancy-related deaths, ending preventable newborn and under-five deaths, cutting down on the fatality rate of various diseases and so on [2]. In the past half century, the world's average life expectancy has increased from 52.62 years in 1960 to 69.64 in 2010; the global health level has generally improved, but the growth rate has been slowing down. Meanwhile, the growth rate of the less developed areas has been greater than that of the developed areas. Although life expectancy between the two shows a narrowing trend, there is still a huge gap in the life expectancy of countries [3]. Life expectancy in most developing countries began to increase rapidly after World War II because of the sharp decline in mortality [4], especially in China and India, the most two populous developing countries, health improvement of which contributes greatly to the improvement of global life expectancy [5]. Therefore, the improvement of global life expectancy mainly depends primarily on developing countries. Prior studies have shown various factors like natural environment, economic development level, and living habits etc. are related to life expectancy, and have illustrated their distinct effects in more- and less-developed countries and regions [6; 7; 8; 9; 10; 11; 12; 13; 14]. As human beings face increasing challenges in the process of increasing life expectancy, countries and regions need to take comprehensive measures, including developing their economies, formulating health policies based upon their own specific conditions, improving the environment, and promoting social progress, so as to effectively maintain the continuous improvement of life expectancy [6; 7; 8; 9; 10; 11; 12; 13; 14]. For Chinese government, extending life expectancy and promoting public health and wellbeing are also two major concerns. It was proposed in the 13 th Five-Year Plan to extend national average life expectancy by one year from 2015 to 2020 [15]. Moreover, increasing life expectancy is also one of the main indicators of \"Healthy China 2030\" [16]. Since the establishment of new China, life expectancy has been increasing a lot, from 35 years old in the early days of the establishment of new China to 68 in 1982, further reaching 74.8 years in 2010. In addition, the growth rate began to slow down when life expectancy reached about 70 years, which is similar to many developed countries [17]. Meanwhile, the growth rate of the less developed areas is greater than that of the developed areas, because of which the regional inequality of health level has been effectively alleviated, but a gap remains in comparison to developed countries. There is still room for further improvement in China's health inequality [18]. Various empirical studies have clarified differences in the upside for life expectancy in regions with different economic development levels [19]. Meanwhile, factors influencing life expectancy are also different in different regions and at various development stages [1; 20; 21]. Therefore, how to further improve life expectancy in different regions when the current life expectancy has reached a certain level depends mainly on the local governments. They must scientifically assess the dynamics of life expectancy and its causes, which is fundamental for setting reasonable goals and formulating effective policies to increase life expectancy. Most previous studies focused primarily on using cross-sectional data to explore the factors of life expectancy in a certain year or on using panel data to analyze the influencing factors in a certain period of time.