Abstract: The secondary forest is the main forest type formed after natural forest cutting, which is significantly different from the primary forest and artificial forest in many aspects, such as stand structure and species composition, forest growth and productivity, stand environment and ecological functions, etc. Therefore, studying the health diagnosis, classification and evaluation index, community structure and ecological functions, and soil ecological processes of the secondary forest ecosystem are of great significance for biodiversity protection, ecological security, ecological barrier construction and ecological civilization construction in China. Based on the extensive collection of the latest literature on secondary forest research at home and abroad, this paper discussed the diagnosis, classification and evaluation method of secondary forest, community structure and ecological function, as well as the impact of forest restoration process on secondary forest, etc. At the same time, this paper explained the basic scientific issues concerned in the research of secondary forests, and proposed future research directions for the secondary forest, which would provide scientific basis for the multi-purpose management of secondary forest, ecosystem management, and natural forest protection and restoration in China.