AbSTRAcT Modern urban planning science is structured on the classic physics-based traditional rationality. However, ever since 1980s, an age of multiple urban chalenges, the urban planning science based on traditional rationality has also been facing tremendous blames and the risk of fragmentation. On the other hand, the post-modernism are al-inclusively capturing fields of urban society, urban culture, mental development and urban equality, which were excluded from traditional rational planning. Urban plans tend to be non-rational political guidelines that it is commented that if urban planning is everything, it is nothing(A·Wildavsky,1973). The neo-rationality based on the Complex Adaptive System (CAS)theory pays due attention to the critical elements overlooked by traditional rationality, such as individual autonomy, adaptability, accumulative learning, collective decision-making, intergrowth with surrounding environment, occupying ecological niche, autonomous recessive orders and "connecting summation". It is illustrated that neo-rationality tolerate with the rational principles of traditional rationality as well as include the advantages of post-modernism. It preliminarily established a new theoretical framework under which, consecutiveness and non-consecutiveness, determinacy and indeterminacy; divisibility and non-divisibility, predictability and unpredictability could co-exist. It is concluded that following the approaches of neo-rationality, modern urban planning science is walking out of the trap of "failed" rationality.%现代城市规划学的内核是由经典物理学为核心的传统理性主义构建的。但进入20世纪80年代以后，在诸多现实的城市问题挑战下，以该方法论为基础的城市规划学遭受空前的责难而支离破碎。而另一方面，后现代主义以包罗万象的姿态对传统理性主义所不能包容的城市社会、文化、精神、公平等领域进行“占领”，城市规划逐渐变为非理性的政策纲领，以至于有人提出这样的感叹“如果规划什么都是，那么它也许什么都不是”（A·Wildavsky,1973）。以“复杂自适应系统理论（CAS）”为内核的新理性主义，有效克服传统理性主义忽视构成系统的个体的主动性、适应性、学习积累性、集体决策、与周边环境共生、占领生态位、自发隐秩序和“连接总和”等决定性因素。从而展示出，新理性主义不仅能包容传统理性主义的合理内核，又能吸收后现代主义的某些养分，初步构建了连续性与非连续性并存、确定性与非确定性并存、可分性与不可分性并存、预见性和不可预见性并存等的新理论框架。由此可见，只要遵循新理性主义给出的轨迹，现代城市规划学就有希望走出“理性”遭到毁灭的歧路。
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