Abstract: In order to effectively reduce disaster losses caused by fog and haze, and provide a reliable basis for haze weather forecast, a durative regional fog and haze weather occurred in Shaanxi Province in December 17th -25th, 2013, was analyzed by using MICAPS data, automatic weather station data and laser radar data. The results showed that: the persistent fog and haze process had obvious phase characteristics. The configurations of high and lower level were conducive for the quick accumulation of fog and haze in the early stage. In the late stage, the 500 hPa circulation at mid-latitude was straight, and there was a weak warm advection at 925 hPa, which were favorable for the persistent fog and haze process. Persistent fog or haze process had low requirement for thicker wet layer, and the thickness of wet layer under 900 hPa and the relative humidity from 60% to 80% were advantageous to the lasting of fog and haze weather. Weak surface wind, the maintaining of temperature inversion, and the pollutants concentration in the surface below 200 m were the main weather features of this serious fog and haze process. The vertical distribution of vorticity advection and total temperature advection provided favorable dynamic and thermodynamic structure for the generation and maintaining of fog and haze, the special terrain of Guanzhong Area was another important reason.