Based on the Sino-US Forest Health Cooperation Program, along with review on lots of foreign and domestic literatures, the historical trends of attributes of forest and the concept of health in the modern society are discussed and the concept of forest health is redefined, combining the methods of logic discursion with demonstration analysis, qualitative analysis with quantitative analysis and the ecology with other related science from point view of macro and middle scope aspects. This paper tries to develop the theoretical system of forest health based on the situation of China's forestry for the first time and build assessment approaches on forest health. Combining the literature review, forest health appraisal of urban forests, shelter forests of farm land, Masson pine forests and Bamboo forests of Phyllostachys praecox f. preveynalis for bamboo shoots are validated theoretically. A case study on forest health assessment is conducted on Chongdungou of Jiangxi Province. The main conclusions are as follows:1. The forests are of not only environmental and resource attributes, but also the ecological infrastructure in modern society, which is more important and expresses some special structure.2. Forest health is characterized by complexity of nature and society, non-linear, multi-dimensional and dynamically stable properties.3.The disturbances of forest health in China includes the conversion of barren land to forest dominated by human beings, lack of silviculture operations, increasing pressure of forest utilization requirement, such as timber demand and encroachment of forest land, high risk of exposure caused by domestic and international trade and severe pollution, climate change and intensive public attention.4. Theoretical research on China's forest health must be based on the situation of process of forest restoration, restructuring of forest landscape, high ecological risks and high pressure of utilization.5. The forest health fundamental theory has been developed, which includes the attributes of forest health, supporting theories, main disturbances and assessment methods. The concept of forest health is defined as the condition and productivity of forest to supply the necessary ecological service whilst maintaining healthy growth and vitality to regenerate.6. Two preliminary theoretical models for forest health assessment have been developed according to the characteristics of appraisal object. The key element method is suitable to assess the forest ecosystem with relative simple structure or in small scale by assessing the suitability, safety, stabilization and succession of advantageous tree species and forest structures. The Symptom/Service approach is suitable for assessing the forests with more complex structure or in large scale.7. Criteria of forest health used in USA and other developed countries, containing 23 criteria categorized into forest productivity, biodiversity, forest health and vitality, soil conservation, water conservation, and carbon cycle, are introduced.8. Concept and application terms of forest health condition and forest health trend are put forward. And forest health condition is further divided into certainty health condition, which includes healthy, inferior-healthy and unhealthy, and uncertainty health condition. For the forest health assessment of forest restoration, it is more suitable of using forest health trend according to the study.9. Based on the assessment of urban forest, shelter forest of farmland, Masson pine forest, Bamboo forest of Phyllostachys praecox f. preveynalis for bamboo shoots, and the case study in Chongdungou of Xinfeng county, Jiangxi province, this paper concludes that forest health assessment is not very hard by qualitative assessment after the better understanding of the forest ecosystem. It's capable of qualitative assessing forest health in a relative complex forest ecosystem, but can find the trend by continuous monitoring.