Abstract: Objective To investigate the associations of air pollution with blood pressure in middle and old-aged hypertensive patients in Beijing. Methods A total of 85 local residents of hypertension aged 45 to 85 years old and with good physical activity in Beijing was recruited. Exclude patients with other serious cardio-pulmonary diseases, infections, or allergic diseases. We collected the 24 hourly concentration of PM2.5, PM10, SO2, NO2, O3 and CO from the nearest Beijing monitoring sites for 5 days. Linear mixed effect model with a random intercept for each participant to account the dependent repeated measures was used to estimate the associations between 6 air pollutants and blood pressure. Results In the single-pollutant model, short-term exposure to 6 pollutants except O3 resulted in an increase in SBP（P < 0.05）. PP decreased with O3 exposure（P < 0.05）and increased with SO2 exposure（P < 0.05）. Conclusions Short-term exposure to air pollution may significantly elevate the SBP and PP of hypertensive patients.

Key words: Key words: air pollution, blood pressure, mixed model, panel study