Based on meteorology and environment monitoring data in January, 2008 in Liaoning central region, a typical haze weather process was analyzed. The results showed that haze was formed due to the stable weather condition in the earth surface and upper air layer in Liaoning central region. Especially because that the weakening of atmospheric dispersion ability in the urban boundary layer that was 500m under earth surface, caused the pollutant in the air cannot disperse. Thus, it resulted in the deterioration of air quality, increase of concentration of particulate mass, and declination of visibility. And in the end, haze formed.