Abstract: Large-scale sports events can create good social and economic benefits for urban development, they may also bring risks to the urban ecological environment to a certain extent though. Using the methods of literature, expert survey, and analytic hierarchy analysis, this present paper analyzes the types of ecological risks, risk sources and risk suffers related to large-scale sports events in host cities, and constructs an ecological risk assessment system consisting of 4 first-level indicators, 14 second-level indicators, and 40 third-level indicators. The results show that the ecological risk types of large-scale sports events in host cities are mainly divided into ecological imbalance risk, ecological space occupation risk, environmental pollution cumulative concentration outbreak risk, resource and energy disordered excessive consumption risk; ecological environmental indicator is the primary factor that causes urban ecological risk, urban ecological space indicator the second factor, and ecological population and energy resources indicator the third and the fourth factor respectively. The results suggest that in the process of undertaking large-scale sports events, we must first strengthen the prevention and control of urban ecological environment pollution; secondly, we must do a good job in urban construction planning to prevent the deprivation and coercion of urban ecological space and ecological environment; and next reasonably control the size of migrant population; finally, we must improve the residents' environmental awareness to build an ecological and social action system involving the whole population.

Key words: large-scale sports events, ecological risks, sustainable development, risk source, risk suffer, index system