Urban is a typicallycomplex system of self-adaption. It presentsa nonlinear feature during its evolution progress. This feature determines that the top-down regulatory planning can only work in particular conditions. Most of the time, urban evolution is self-organizing and adaptive, sometimes even makes automatic adjustments and changes. In complexity science, such spontaneous evolution mechanism is called self-organization. Based on self-organization theory, this paper makes a case study on Beijing South Luogu Lane to explore the generative mechanism of self-organization during the urban evolution. This paper mainly concerns three questions: how self-organization happens during the urban evolution? What social effects self-organization will bring? What is the relationship between self-organization and the top-down regulatory planning and system design?

This paper applies methodologies of questionnaire and review to explore the above three questions. Reviews are used to explore the individual behavior, group behavior and the understanding on the institution during the evolution of South Luogu Lane. Questionnaires are used to explore the roles of planning, institution design and social effects brought by self-organization development.

Surrounding the above three research questions, this paper divides the evolution of South Luogu Lane since the founding of China into three periods. First isthe quadrangle period. Second is the illegal construction and environmental deterioration period. Third is “organic renewal”and gentrification period. Analysis shows that self-organization mechanism is essential to the evolution of South Luogu Lane. When the changes of macro condition break thesystem equilibrium, the individuals will automatically respond to these changes in a rapid, selfish and spontaneous manner. The individual behaviors accumulate to group effects which cause mutations at a macro level. Such mechanism explains the formation of quadrangle, commercialization and gentrification in the South Luogu Lane. During the process of self-organization, the regulatory planning and system in effect breaks the system equilibrium and triggers the changes of self-organization. Despite that self-organization promotes the formation of order in complexity science, researches show that self-organization may bring negative effects during the urban evolution. Therefore a proper use of the planning and institution is significant to the benign development of urban self-organization.

This paper illuminates the general mechanism of self-organization during the urban evolution: the breaking of system equilibrium–the responding of individual behaviors –group behavior – macro mutation effect. The paper also demonstrates the correlation between individual behavior, group behavior and institution and planning, which provides supports for the decision making of urban planning under complex conditions.