(1) Primary stage of theoretical research on continuing education (from the early 20th century to the late 1950s) In the primary stage of theoretical research on continuing education, the level of research on continuing education by individuals and groups is still relatively low, at the primary level. It has achieved initial results in learning objectives, learning ability and adult education. The theoretical research in this period mainly shows the following characteristics: First, the research method is simple, the logic is not strict enough, and the research results are quite different. Second, the research problems are scattered, unsystematic and not in-depth. Third, researchers only pay attention to the psychological research of adult learning and ignore other studies, such as historical research and philosophical research. Fourth, most of the research results are obtained by sociologists. Fifth, the research is mainly concentrated in a few countries, such as the United States, Britain, the former Soviet Union, Yugoslavia and other countries. Sixth, the research scale is not large, the progress is not fast, and the development direction of continuing education theory research has not really been shown.

(2) The development stage of continuing education scientific research (1960s to present). Since 1960s, the theoretical research of continuing education has entered a period of qualitative leap development. As the world economy and society put forward higher requirements for continuing education, the practice field of continuing education has been developing and the research scope has been expanding and deepening. In particular, the concept of lifelong education has been accepted by more and more people, and the position, function and methods of continuing education in the economy and society have been preliminarily understood and practiced, and the scientific research of continuing education has also made great progress. Social scientists and continuing education researchers have made great contributions to continuing education from different angles, levels and aspects. For example, the book "Adult Education-An Overview of a Forming University Field" not only summarizes the achievements made by research institutions of adult education and continuing education and the basic understanding of experts and scholars in this field, but also expounds the nature and scope of adult education and continuing education as special research fields of universities. In the 1960s, Marcand Knowles, the most famous educator in American education, proposed to attach importance to the personality and advantages of adult learners. By the mid-1970s, scholars in the former Soviet Union attached great importance to the psychological experimental research on adult intelligence, and successively published monographs such as The Development of Adult Physiological and Psychological Functions, Questions about Modern People's Learning, and Adult Learning Psychology, which enriched the theory of adult learning and education.

The popularization of lifelong education has played an important role in promoting the further development of continuing education research. The book Introduction to Lifelong Education, published by French educator Paul lengrand in 1970, and the Report on International Education Strategy (entitled "Learn to Survive") submitted by the International Education Development Committee to UNESCO in 1972 all proposed that the traditional school education system must be replaced by the lifelong education system and eventually move towards the development direction of a "learning society". This is of great significance to the sustainable development of continuing education and adult education research.

Since the 1970s, the research on the relationship between continuing education, adult education and social structure and change has gradually become a research hotspot. Paulo Flair, a famous Brazilian educator, believes that the primary task of adult education and continuing education is to promote social and political changes, which has been widely recognized in developing countries.

Since the 1980s, the most striking development of international continuing education research is reflected in two aspects: First, the extensive development of comparative research on continuing education in the international scope has strengthened the need for countries to communicate with each other and learn from each other's strengths, making international conferences, cooperative research and information exchange on continuing education unprecedentedly active. The other is the revival of Marxist theory in the field of western continuing education. Some western scholars began to use or draw lessons from Marxist viewpoint to control and influence the process of continuing education, which injected new vitality into the research of continuing education.

To sum up, the theory and research of continuing education abroad have the following characteristics: first, the discipline of continuing education has been established and developed; Second, establish specialized research institutions and organizations; Third, its research has received universal attention and support from all countries; Fourthly, the international comparative study of continuing education has been widely carried out.