改革开放以来，中国社会结构的快速转型几乎成为当前中国社会变迁的一个重要标识。大都市作为承载现代化的符号，在各种新旧体制、机制的交织作用下，分化出了一个庞大的底层群体，并逐步衍生形成一个社会学意义上的“底层社会”。本文通过对上海市的实证调查，从理论和经验不同角度揭示了现阶段我国大都市底层社会的形成原因及其发展样态，并对其可能产生的社会影响及对大都市发展的带来挑战进行了分析。

Since the reform and opening up, the rapid transformation of Chinese society has almost become an important structure to identify the current Chinese society. Metropolis as a sign bearing modernization，in the intertwined role of various new and old systems, produce a large of low-income population, which gradually form a "underclass society" in sociological sense. For in-depth understanding of underclass society in metropolis，we selected low-income population in Shanghai as respondents, trying to use a different perspective to analyze reasons of formation and impact of the underclass society in metropolis .