Prof. Hou works at the Institute of Chinese Historical Geography at Fudan University, Shanghai, China. His major research field is Chinese Historical Demography or Population History, Chinese Medicine History. The project for the first time suggests that the demographic transition of China began from the first half of the 20th century, and it appeared with the changes in the treatment of epidemic diseases. With the introduction of modern public health, the modern transportation system, and the popularization of these systems from the cities to the countryside, from coastal areas to the inland areas, China began to experience the demographic transition, mainly exemplified by the drop in the mortality rate. The demographic transition for the first time freed China from the model of high fertility and high mortality unchanged for a long time in the history, and is the direct reason for the quick growth of Chinese population henceforward. This project is a systematic and complete research on Chinese population of the first half of the 20th century. It is an interdisciplinary research combining the research methods of historical studies and demographic studies.