Based on the conventional data, sounding data, AMS (Automatic Meteorological Station) data and air quality data, a haze event happened in the southwestern Shandong Province in June 2007 is analyzed. The results show that the formation of the haze is related to various meteorological factors. The warm continental high pressure moved eastwards into the sea, and the lowtemperature and highhumidity air was transported to Heze by the easterly airflow at its bottom, which were beneficial to the formation of the haze. The wind speed at the midlow level was small, and the wind direction was reverse with altitude, in which the wind field was also beneficial to the formation of the haze. The stable atmospheric stratification and inversion layer existed at lower levels are important factors to the formation of the haze, and the high concentration of pollutants is also the base of the haze.