| Sixty years after the Second World War, Taiwan's population had greatly changed. At the early time of the post-war, the demographic change in Taiwan was in the initial stage. But the years between 1961 and 1975 were the critical stage for Taiwan's traditional demographic change. And then until 1985, the demographic change finished. Taiwan's total fertility had declined below the replacement level in 1985, and continued to descend. The total fertility was 1.1 in 2007. At that time, Taiwan was the same to the Republic of Korea, Japan, Singapore and other developed countries naming ultra-low-fertility regions.According to the theory of sustainable development that human beings are the components of the natural - economic - social complex systems. Human's survival and development have to rely on the resources and the environments. On the other hand, the normal operation for the economy and society also need a number of the population. But there are some deviations between the Taiwan's the current population and sustainable development. We need to make the population return to the normal level for the socio-economic development. As we all know that if we want to find the method for promoting the fertility, we first need to make clear the factors constraining the fertility. In this paper, we hope to find out them.At the other side, the phenomenon of declining birth rates has become a worldwide population phenomenon. It brought about great challenges for the world's population development. Exploring the underlying factors for the fertility declining can also give some helps to improving the current population situation in the countries or regions.In this paper, the innovations are the ability to join the political economy aspects of the productive forces into the discussion framework on the base of summarizing and evaluating the results of previous studies. It focuses on studying the fundamental driving force for fertility declining. This article holds that the fertility declining is the results led by a number of factors, including power systems generating power, passing through the support system, and ultimately completing by the operating system.Finally, the author carries out an empirical analysis of the population changes in Taiwan according to results of the theoretical analysis that the impact factors for the fertility declining. We find out that the changes in Taiwan's fertility can support that the development of scientific and technological progress and productivity is the deep-seated causes of promoting fertility reduction in Taiwan's effectively. |