Observation of surface concentration of particulate matter (PM10, PM2.5) and meteorological parameters, including visibility, relative humidity (RH), precipitation, and wind speed (WS) from 2008 to 2010 were analyzed in Shanghai, China. The haze events are identified as the following: (1) Severe haze (visibility < 2 km) occurs frequently when PM10 and PM2.5 are above 181 and 115 µg/m3, respectively, with RH in between 78%–90% and WS ≤ 0.6 m/s; (2) Moderate haze (2 km ≤ visibility < 3 km) occurs frequently when PM10 and PM2.5 are greater than 114 µg/m3 and 96 µg/m3, respectively, with RH of 67%–90% and WS ≤ 1.0 m/s; (3) Mild haze (3 km ≤ visibility < 5 km) happens when PM10 and PM2.5 are greater than 96 µg/m3, 71 µg/m3, respectively, with meteorological conditions of 72% ≤ RH ≤ 90% and WS ≤ 1.0 m/s; (4) Slight haze (5 km ≤ visibility < 10 km) happens when PM10 and PM2.5 are higher than 80 µg/m3, 54 µg/m3, with meteorological conditions of 66% ≤ RH ≤ 90% and WS ≤ 1.3m/s. A typical haze event was analyzed during the MIRAGE-Shanghai field campaign (September, 2009). The results show that fine particles play very important role in haze formation. WRF-Chem, an on-line regional chemistry/transportation model was applied to simulate the haze event and its related meteorological conditions. The mass concentration of aerosol during the haze period of simulation agrees relatively well with that of observation, suggesting that the WRF-Chem model is reliable for aerosol forecasting over Shanghai. It also indicates that the implementation of combination criterion of PM2.5, RH, and WS is a potential solution for numerical forecasting of haze event.