Articles from Annals of the Association of American Geographers (AAG) address advanced knowledge in all facets of the discipline, and reflect the development of American Geography from one aspect as well. All the articles of Annals of AAG since its first publication have been searched and the statistical analysis of them are carried out, this article summarizes the changing rules of research development of American Geography during the past hundred years, including the status of geography in whole American society, structure of fields and subject in different phases. The conclusions brought about are as follows:(1) American Geography experienced three periods in the 20th century(prewar preliminary development period, postwar clipping development period, and persistent development period ever since 1980), and prosperity of American Geography in the 21st century is foreseeable. (2)Five major fields of American Geography are Environmental Sciences; Methods, Models, and Geographic Information Science; Nature and Society; and People, Place, and Region; and Integrated Geography.(3)Significant research problems and issues about human development are chronically concentrated on,and Human Geography is the main study area.(4)Geographers put much attention to practice, and insist that theories should come from practice then be applied practice. (5)The study fields and structures are steadygoing and more reasonable with past time, although the importance of each field is always varying. (6)According to relative proportion of articles numbers, the development venation of American Geography can be generalized as Nature（1911-1915）→Economy（1916-1920）→Nature（1921-1925）→Cartology（1926-1930）→Place（1931-1935）→Nature（1936-1940）→Geography Education（1941-1945）→Environment（1946-1950）→Place（1951-1955）→Economy（1956-1975）→Nature（1977-1990）→Economy（1990-2005). The variety of study subject mentioned above can also represent the holisticdevelopment rule of World Geography.