Abstract: In this paper, we have solved the motion equation of the at mospheric boundary layer under the geost rophic momentum approximation when a front exists. and obtained the characteristics of the stream field of the cold front in the boundary layer, for example, the slope of the cold front increases with the increases of geostrophic vorticity, the tendency of the geost rophic wind speed, and also increases with the decrease of the thermal wind speed along the motion direction of the front. The stream field below and above the cold front surface in the boundary layer depends on the slope of the front, the geost rophic wind speed and its temporal and spatial distributions. The common characteristics are that there exists updraft motion above the cold front surface and downdraft motion below that.