Abstract: During 2005 the Solar activity level was very low, since this year February the monthly mean F10.7<100. At August 24 a severe geomagnetic storm event (Kp=9) occurred with a sudden commencement. This is a good case for the analysis of the influence of a severe geomagnetic storm on the density of the upper atmosphere. In this paper the measured data of the satellite borne atmospheric density detector. From analyzing these measurements the following results were concluded. During this severe geomagnetic storm event, the atmospheric density showed strong disturbances. There are two responses, one is a global thermosphere density enhancement follow the variations of the geomagnetic disturbance, the responding processes were 6 hours late after the geomagnetic disturbance started, the biggest change ratio is 2.5. Another is abnormal density disturbance at high latitude areas during the peak period of geomagnetic disturbances, the biggest change ratio is 5.5, and with an asymmetry feature for the sauthern and northern hemispheres. In situ measurements also show that traveling of the atmospheric density disturbance from high latitude to lower latitude region very fast, the velocity is about 15 º(latitude)/h at middle latitude region.