Abstract: Traffic congestion has become the bottleneck restricting the sustainable development of small-and-medium-sized cities. Traffic chaos is one of the potential causes of traffic jams. Based on the triple spatial logic in theory on production of space, this study is devoted to revealing the spatial law and driving forces of traffic disturbance in small-and-medium-sized cities. It is found that road misappropriation and disordered driving are the main spatial characteristics of traffic chaos; based on different types of traffic and road space, they can be summarized as three types of road encroachment and two types of unordered driving patterns. Road encroachment is the direct cause of disordered driving, and it appears as a space-effect path from the outside to the inside under the cross-section of the road. The fundamental causes of traffic chaos in small-and-medium-sized cities are the spatial order of legal ideas and the unity of space perception and action of traffic subjects; traffic influencers invade and occupy traffic space, the traffic awareness of non-motorized drivers and pedestrians is weak, and traffic law enforcement personnel do not enforce laws closely or failure to comply is the direct cause.