The biomass, growth, annual litter fall, main nutrient contents, and the influences on soil nutrients, soil microbes and soil biochemial activities of secondary forests in Xishuangbanna were studied. Results showed the characteristics of uptake, accumulation and return of biological materials and nutrients in secondary forests, and their effects on soil nutrients. Microbe decomposition of litter fall and biological nutrient cycling of secondary forests were also dealt with. The study provided a basis for further research of tropical forest ecosystem. The plants grew quickly in the tropical secondary forests. The uptake of nutrient elements was large and its proportion of return to uptake was about 0.5. A great quantity of nutrient elements was accumulated in plants with increasing age of trees, and soil nutrient content was low. With increasing age of secondary forests, uptake, accumulation and return of nutnent elements increased, the intensity of litter fall decomposition increased and the speed of material cycling was quick.