Haze weather is becoming one of the biggest problems in many big cities in China. It triggers both public anxiety and official concerns. Particulate matter (PM) plays the most important role in causing the adverse health effects. Chemical composition of PM2.5 includes primary particles and secondary particles. The toxicological mechanisms of PM2.5 to the human body include the oxidative stress, inflammation and carcinogenesis. Short or long-term exposure to PM (especially PM2.5) can cause a series of symptoms including respiratory symptoms such as cough, wheezing and dyspnea as well as other symptoms. There are positive associations between PM2.5 and mortality due to a number of causes. PM2.5 is considered to contribute to the onset of asthma, the exacerbation of chronic obstructive pulmonary disease (COPD) in haze weather. Some approaches including outdoor health care, indoor health care and preventive medications can prevent the patients with chronic airway diseases from exacerbations.