Invasive species pose risks to regional economies and public health as well as imposing serious damage to natural ecosystems. Urban ecosystems are more susceptible to biological invasions than other ecosystems because they are subjected to more frequent human disturbances. Green space acts as important channels for the spread of alien species into urban ecosystems. Risk analysis can be an effective tool used for preventing invasion of alien species. Although various risk analysis systems have been developed for agricultural and forest ecosystems or nature reserves, the domestic effort to manage risks associated with invasive species in urban green spaces has been limited in China. Therefore, there is a pressing need for formulating scientifically sound methods and approaches for risk analysis in this emerging field. Here, we presented a risk analysis system including risk identification, assessment and management for biological invasions in urban green spaces. Based on risk identification for alien species, we established a risk assessment index that consisted of 4 different layers, i.e. object, item, factor, index layers. A total of 26 index parameters were proposed to assess the risk level, which originated from the risks involved in introduction, colonization, spread and damage of alien species in urban green spaces. In addition, methods for index quantification, weight setting, modeling and risk grading were presented. Applying this system, we analyzed the risks of alien pest species potentially attached to trees brought from Japan to China to green landscapes for the 2010 Expo in Shanghai. Our results showed that 7 species posed a high risk (4 insects, 2 plant pathogens, and 1 plant nematode), 10 species a moderate risk (3 insects, 4 plant pathogens and 3 plant nematodes), and other 2 species (1 insect and 1 nematode) a low or extremely low risk. Based on this analysis, risk management measures were suggested to help local policy-makers set priorities for the management of these alien pests. Monitoring did not reveal the presence of any invasive pests during or after the Expo, suggesting that the risk analysis system may have provided an effective tool for preventing the introduction of invasive alien species and effectively ensuring the ecological security of the 2010 Expo, Shanghai, China.