In order to deepen the understanding of the research progress of urban sprawl, this study analyzed international research progress and trends of urban sprawl since the 21st century by using knowledge mapping, based on the "Web of Science" data and CiteSpace software. The results show that: (1) The number of published literatures on urban sprawl is generally on the rise, and the papers are mainly published in urban or geography journals. (2) There is a close cooperation among countries in the urban sprawl research, but the cooperation among institutions and the cooperation among authors are both insufficient. The most active country, institution and author engaged in urban sprawl research are the United States, the Chinese Academy of Sciences and Salvati respectively. (3) Based on the high-frequency keywords such as city, growth, land use, urbanization, the United States, patter, China, impact, region, GIS, etc., three different research stages (initial exploration period, high-speed development period and continuous development period) have been formed. (4) In the early days, the related research mainly focused on the single field of urban sprawl. However, it has gradually turned to the interdisciplinary research which is combining urban sprawl with other fields recently, such as landscape ecology, human health, land finance, etc. Compared with the existing urban sprawl review, the innovation of this study is that we use a new method which combines quantitative analysis of knowledge mapping and qualitative analysis. In the future, the research trends of urban sprawl will be mainly reflected in the expansion of research fields and cooperation networks, innovations in research methods, and increased multi-scale research.
