Abstract: In order to promote comprehensive and in-depth research and practice of balanced and adequate development of libraries in academic circles, the connotation and extension of the concepts of balanced and adequate development of libraries are defined by referring to existing relevant achievements on balanced and adequate development of economy, public culture, education, medical and health, as well as the effective allocation of information resources, and balanced and adequate development of basic public cultural services of libraries.It is believed that balanced development of libraries means that the supply and demand of library resources are equal or roughly equal under economic, political, cultural and social development and ecological civilization construction objectives in a specific period. Adequate development of libraries means that the number of libraries is sufficient and their qualities are good enough to fully meet the goals of China's economic, political, cultural and social development and the construction of ecological civilization, and to fully meet the needs of people for a better cultural life. The balanced and adequate development of libraries means that libraries have achieved both balanced development and adequate development. The relationship between the balanced development of libraries and the adequate development of libraries is mutually supporting and promoting. The balanced and adequate development of libraries is not only a dynamic process, but the goal that libraries are constantly pursuing. The results of theoretical research and practical exploration on balanced and adequate development of libraries can not only promote the prosperity and development of libraries in our country, but also show the world China's unique theories, thoughts or concepts of library science.