Automatic keyword extraction is to extract topical and important words or phrases form document or document set. It is a basic and necessary work in text mining tasks such as text retrieval and text summarization. This paper discusses the connotation of keyword extraction and automatic keyword extraction. In the light of linguistics, cognitive science, complexity science, psychology and social science, this paper studies the theoretical basis of automatic keyword extraction. From macro, meso and micro perspectives, the development, techniques and methods of automatic keyword extraction are reviewed and analyzed. This paper summarizes the current key technologies and research progress of automatic keyword extraction methods, including statistical methods, topic based methods, and network based methods. The evaluation approach of automatic keyword extraction is analyzed, and the challenges and trends of automatic keyword extraction are also predicted.