自然保护区开展生态旅游给环境带来了许多负面影响，将旅游活动限制在承载力内是生态旅游持续发展的基础。不同的旅游生命周期阶段，承载力不同，本研究利用环境科学中正在兴起的生命周期评价手段，对旅游发展不同阶段的承载力作出科学评估。在此基础上，利用现今比较成熟的风险分析方法，对生态旅游活动对环境的影响进行风险评价。

Ecotourism is kind of indirect use of natural resources compared with those direct use ways such as farming, stockbreeding, hunting and logging, which could bring positive impacts to natural resrouces conservation.However, it also could bring negative impacts and even resources degradation due to poor management. Therefore there exists environmental risk for nature reserve to develop tourism. In order to assess the environmental impacts, the research selects Jiuzhaigou Nature Reserve as the case study area to conduct the impacts assessment from social economical and ecological environmental aspects, respectively. In social economical impacts assessment, the Travel Cost Mothod of environmental economics is used to evaluate the recreational benefit of natural resources, and the recreational value is used for comparative analsis with the benefits from traditional resources utilization. The ecological environmental impacts assessment is conducted at two scales, ecological factors and landscape scale. In the ecological factor scale, the Trail Assessment Method is proposed for the non-pollution ecological impacts assessment, which provies a practical monitoring method for nature resever's daily management. In the landscape scale, two-year remote sensing images of 1991 and 1997 are interpreted respectively, and the landuse changes and vegetation changes are comparatively analysed using landscape indicators..The second part of the research is related to tourist carrying capacity study. Based on ecological and social psychological analysis, the new concept Limit of Acceptable Change is adopted instead of Carrying Capcity. The study shows that it's impracticable to set up a fixed tourist number for a tour site. The only way is to use the adaptable ecosystem approach to adjust dynamically the limit of tourist number according to the ecological environmental monitoring indicators. So establishing a series of indicators which can sensitively reflect the eco-envionmental changes is very important for controlling the tourists within the limit of acceptable environemtal changes..The third part of the research is foused on the alleviation of environmental impacts caused by tourism. The study is conducted from two aspects: one is using institutional economics and game theory to analyze local community participating in the conmmon resources management and utilization; the other is applying organazational behavior sciences to study the management model for the common resources in nature reserves. .