Based on the routine observation synoptic charts and the synoptic charts at 500 hPa from 1988 to 2007, the temporal distribution, meteorological fields, and the stability factor of haze days during spring and summer are analyzed. The results indicate that the annual haze days increased, and the monthly distribution showed a single peak pattern with high values in December and January. There is a highest probability of haze at 14:00 in winter half year and at 08:00 in summer half year. The haze events in winter half year often occur under the weather condition of weakened cold air, decreased surface pressure, increased temperature, low wind velocity and high humidity. The correlative weather systems include the back of the denatured high, the warm sector ahead of fronts, and the ground inverse trough. Occasionally, haze events happened along with the inrush of cold air with the increasing pressure and decreasing temperature and low humidity, and the correlative weather system is the land cold high. The haze events in summer half year often happened in the morning with high temperature, low humidity and stable atmosphere. The influencing systems (500 hPa) include the subtropical high, the edge of the subtropical high, the weak ground inverse trough, and the dryhot descent flow controlled by a typhoon.