Based on historic visibility data of 12 stations and observed data of visibility, relative humidity, and aerosol during 2009-2011 in Tianjin, the basic characteristics of low visibility is analyzed. In addition, the atmospheric chemical model of WRF Chem is used to simulate the atmospheric horizontal visibility from October 2010 to January 2011 in Tianjin. The results show that low visibility mainly happens in every November to the next January. The atmospheric horizontal visibility can be better calculated on the basis of acquisition of PM2.5, PM10 and the relative humidity. And the use of WRF Chem atmospheric chemical model and fitting formula, the visibility can be effectively simulated and forecasted.