Using the results calculated from the model output production of mesoscale model (MM5) the forecast of heavy fog on the high way in Shaanxi province is made.In the output productions, there are some elements,such as moisture,wind and thermal fields per hour,which a closely related with the formation of fog.Then,using the methods of PPI,MOM and MEC,the fog forecasts of 14 point on four expressway in Shaanxi province can be presented.It is shown that the forecast method is proved to be available.