By using the non-static mesoscale model MM5, the forming process of the occluded front in North China during the period of November 20—21, 1998 was numerically simulated.It is shown from the sensitivity tests that the spatial scale of the occluded front in North China is smaller than that of the ideal .The area of precipitation is contact with the character of the occluded front, and the condensed latent heat affect the maintaining of the occluded front in North China. The topography played a determinant role in maintaining the occluded front in North China. If no topography, the occluded fronted which is weaker will form earlier at the western side of normal place.