Abstract: Using the air quality monitoring data，NCEP reanalysis data and conventional observation data，the characteristic and circulation of consecutive haze process on large－scale in Sichuan Basin from 22 January to 5 February 2014 are analyzed．The results show that the persistent 14 days heavy pollution process occurs under the stable background of zonal circulation in middle－ high latitude．The westerly flow is relative flat and straight wind form the Tibetan Plateau to Basin is not conducive to cold air southward and generate precipitation at the same time，most areas in China is under the control of almost－ same pressure field，that the pressure gradient force and the low level near-to-ground wind speed is very small，it will conducive to the formation and maintenance of haze．Also the change of the atmosphere mixed layer'height is a good indication for the conversion between haze and fog．The haze's mixed-layer-height is higher ，the relative humidity is lower．The difference between temperature and dew－point temperature is larger and the temperature Inversion is weaker than fog's，all of these provide a good reference for forecasting the conversion between the haze and the fog．