旨在以城市重大危险源为主体对象研究出一套科学有效的风险评价方法。通过拓展城市重大危险源的评价技术，提出安全等级“层级叠加”原理，将单独评价拓展为相关耦合评价。研究了城市区域性重大事故风险评价技术及量化方法，以城市地理和城市资源为平台，分析各类灾害发生的可能性，确定种类灾害相对于城市的安全等级，并将其以一定的比例相关系数进行叠加，得到城市安全的综合且近似于实际的安全“图谱”，并综合人口密度分布建立社会风险评价指标，从而对城市危险源进行综合安全规划，并以试点城市为例给出可视化的城市安全等级划分结果。研究工作成果可为相关研究提供参考，为城市安全规划管理提供科学的决策依据，同时对提高我国城市区域性风险评价技术水平，有效预防和控制火灾、爆炸、毒物泄露等重大恶性事故的的发生等方面具有重大意义。

The purpose of the article is to regard city as the object and work out a set of methods of assessment of risk. The improved technology of assessment of risk for urban major hazards and the method of quantization are studied. Principle of “level-superposed” of the grade of security is brought forward. Analyzing the possibility of all kinds of calamities to take place, confirming the grade of security relative to city of the kind calamity, and superposing its coefficient correlation in certain proportion, this paper gets the synthetical security atlas similar to the real one based on urban geography and urban resource. The evaluation index of social risk is set up based on the distributed comprehensive density of population, thus comprehensive safe planning to the dangerous source in the city can be carried on. At last, an example for providing the visual safe grade of city and the divided electronic map is given. The exploration work of this text can offer reference for relevant research work, which is also significant to improve the engineering level of urban assessment of risk, to prevent and control the emergence of great malignants accidents effectively such as fire, explosion, poisonous substance leakage, etc. , and to offer the scientific decision basis for city safety management.