PM2.5 is one of the main pollutants of air pollution. Long-term exposure to high concentrations of PM2.5 polluted environment can easily increase the risk of developing various diseases including cardiovascular disease and respiratory diseases. As the main place for people's leisure and entertainment, the exposure level and health risk of PM2.5 in urban commercial districts directly relate to people's health. Based on the principle of exposure assessment, this paper constructs a method for assessing the health risk of urban public space environment and carries out empirical research on the commercial district of Mianyang by using on-site measurement methods. On the basis of collecting PM2.5 concentration data, combined with the type of crowd activity and stay time, important public spaces in the commercial district are selected for health risk assessment and optimization strategies are proposed. Researches Indicate that the change of PM2.5 concentration in commercial areas is affected by traffic flow and wind direction; there is a high health risk in public spaces where crowds gather and stay for a long time. The research results have important practical significance for improving the public disease prevention ability and health management level in cities.