Over the past half-century, the nexus between risk and prevention has increasingly become a constant preoccupation among many criminal justice regimes around the globe. In China, while the significant rise in crime following the marketization has been envisaged as an important source of risk, a criminal law concept of ‘social dangerousness’ has gained increasing prominence in the country’s crime control, policing and punishment systems. This article aims to shed light on how social dangerousness has been juxtaposed with and informed China’s preventative state through critical inquiry into the police power of arrest. I argue that the recent legal consolidation of social dangerousness as a prerequisite to arrest has enabled this coercive measure to become more preventive in purpose. By creating an ever-expanding purview of arrest, the police become more capable of capturing the largest possible cohort of suspects deemed ‘socially dangerous’. This is exacerbated by the legal opacity and ambiguity of social dangerousness, which allows manipulation and liberal application by police in diverse scenarios. My analysis suggests that the preventive dimension of arrest manifests itself largely as a punitive power, which runs the risk of turning arrest into a ‘punitive-preventive measure’. This will, inevitably, impose the same amount of intrusiveness and harsh treatment on suspects regardless of their risk levels. It is more concerning that the fusion of preventiveness and punitiveness has managed to circumvent close scrutiny of the justification for the preventive end of arrest by failing to see the need for periodic review.