Abstract：The research from self-organization theory has provided very beneficial help to understand the growth mechanism and the power of urban. Many self-organizing urban models have explained the many dimensions of urban growth according to their own perspective of interpretation. In fact, self-organization city models have only shown the macroscopic mechanism and process of urban growth, as for micro explanation based on active agent comes from the study of Complex Adaptive System (CAS) theory and Multi-Agent System (MAS) theory. The adaptability based on active agent is the core concept of CAS theory, thus shows the relationship between the individual active behavior and the system evolution. The characteristic of CAS has many dimensions; firstly, all active agents get effective adaptability to environment, so system has the ability to evolve too; secondly, there is very complicated nonlinear interaction not only among the active agents, but also between the active agents and active environment, which creates the emergence of system; thirdly, interaction among active agents will bring about complex macroscopic phenomena. Based on the study of CAS theory, MAS theory goes further into the analysis on the interaction between each active agent and subsystem agent, so it perfectly builds the inner link among active agents, subsystem and the conversion of system structure and system level, which is in the process of system evolution. In fact, CAS theory and MAS theory are the basis of this paper. Specifically, it is the original dynamic of urban self-organization which results from the active agent's pursuing continuous adaptability; it is internal reason that urban self-adaptability is also the source of urban network's formation and continuous growth. Individual move to city for work in order to improve adaptability by getting the higher economic potential nodes in division of network; enterprises agglomerate in city to get better adaptability by taking advantage of higher transaction efficiency, lower transaction costs and lager market space. In fact, the process of urban self-organization is the same strategy and behavior of individual and enterprise.
