Based on the air pollution data provided by the Tianjin Environment Monitoring Station and the conventional meteorological data from 2000 to 2004，the characteristics of air quality and the causes of air pollution in Tianjin are analyzed. The results indicate that the major air pollutants are SO2 and PM10, and there are obvious regularities in temporal and spatial distributions in air pollution in Tianjin: air pollution is severer in winter and milder in summer; SO2 and PM10 improved distinctly in the central urban area of Tianjin; NO2 deteriorated in some areas; and meteorological conditions are important to air pollution.