In this paper,the principle of artifical fog was discussed. The factors,such as relative humidity(RH) and wind speed which affect the fogs performance were analysed.The statistical results, based on the above-mentioned weather data for the typical southern district city Changsha and northern district city Beijing, show that the humidity of Changsha is more higher than Beijing. Its fit for producing fog in south except at 2：00 p.m.But in North it s no problerm for producing fog at 2：00 and 8：00 a.m.It is feasible for fog formation at 8：00 p.m.The field experiments indicate the RH for producing fog decreased because of the characteristic of open system.The fogs ability of anti-wind is enhanced for the high condensation efficiency and group effect.Therefore,the primary weather condition for fog formation is almost possessed. Its feasible for producing fog in areas of square kilometers.