The haze has brought great harm to the health and social development of residents in recent years. Although the academic community has conducted in-depth research on the causes，composition and consequences of haze，there were still few studies on the risk perception of haze. From the perspective of social vulnerability and constructivity，this paper analyzes the formation mechanism of haze risk perception by using the data of 1656 residents survey from Shanghai in 2018. The study found that urban residents’ haze risk perception has both fragility and constructive mechanisms. The two mechanisms are not independent but have a “superposition effect”. People with vulnerabilities and a constructive environment will show a stronger sense of risk. Finally，this paper argued that strengthening risk communication and promoting the scientific dissemination of weather information and haze knowledge will help to raise residents’ attention to smog risks.