近年来，我国经济高速发展，流动人口数量与日俱增。与此同时，城市流动未成年人的犯罪问题凸显。21世纪以来，北京、上海、深圳等城市的流动未成年人犯罪率居高不下。这种现象不利于这一群体的身心成长和社会稳定。因此，有必要了解影响城市流动未成年人犯罪的风险性因素是什么，以及社工如何强化犯罪流动未成年人正向改变的潜在保护性因素以预防其再犯罪。 本文采用质性研究方法，对8位在北京市A区犯罪的流动未成年人进行了半结构式访谈，了解他们的个人特质、成长经历、家庭环境和社会背景等多方面因素对犯罪的影响。从生态系统理论的视角出发，探索城市流动未成年人犯罪的风险性因素和社会工作的介入策略。研究进一步验证了一些已有结论，并得出新发现，具体如下：（1）城市流动未成年人的犯罪受微观、中观、宏观系统中多种风险性因素的共同影响；（2）微观系统中个人的童年不利经历与其犯罪之间存在联系；（3）中观系统中家庭环境不良是最主要的风险性因素；（4）宏观系统中社交软件的使用和由产业升级带来的人口迁移成为新兴风险；（5）社会工作介入犯罪流动未成年人的服务中可强化其积极乐观的性格、改变现状的决心和自我效能感高等内部潜在保护性因素，以及家庭支持和合适成年人参与制度的推行落实等外部潜在保护性因素；（6）社会工作的介入策略旨在促进服务对象个人素质的提升和助力服务对象所处环境的改善。基于研究发现，从补充现有的社会工作介入服务和推动城市流动未成年人保护政策和制度的出台这两方面提出社会工作干预和预防城市流动未成年人犯罪问题的建议。

In recent years, China's economy has grown rapidly, and its floating population is increasing. At the same time, the issue of migrant juvenile crimes in cities is prominent, as evidenced by the stubbornly high rate of such crimes in Beijing, Shanghai, and Shenzhen since the start of this century. This issue damages the physical and mental health of juveniles and also social stability. To address the problem, we need to understand what factors drive migrant juveniles to commit crimes and work out solutions for social workers to better help juvenile offenders make positive changes in their lives to prevent them from committing crimes again. This paper, which is underpinned by qualitative research, conducts a semi-structured interview with eight migrant juveniles who committed crimes in District A of Beijing, and analyzes the connections of their personal characters, experiences, family environments, and social backgrounds with their crimes. Then the paper discusses the factors of driving such crimes and the intervention of social work to prevent the crimes from the perspective of the ecosystem theory. Beyond verifying some existing views, the paper puts forward the following new ideas: (1) The offenses by migrant juveniles in cities are influenced by factors at three levels: macroscopic, mesoscopic, and microscopic; (2) At the macroscopic level, adverse experiences in childhood have some connection with juvenile crimes; (3) At the mesoscopic level, the unfavorable family environment is the leading factor of juvenile crimes; (4) At the microscopic level, the usage of social software and the population migration driven by industrial upgrading become a new risk factor; (5) Social work intervention for migrant juvenile offenders can make use of their positive attitude, resolution to mend their ways, and high sense of self-efficacy, as well as family's support and the system of requiring the presence of appropriate adults; (6) Social work intervention aims at improving the personal quality and environment of juvenile offenders. Based on the research, the paper presents suggestions on social work intervention and prevention of migrant juveniles from committing crimes in cities from two aspects: adding social work intervention services and promoting the release of policies and systems for protecting migrant juveniles in cities.