Abstract: A major Stratospheric Sudden Warming (SSW) in January 2009 was the strongest and most prolonged on record. In the period of this warming event, the solar activity and geomagnetic disturbance are extremely low. Hence it provides a good opportunity to investigate the response of the ionosphere to SSW event. The Kriging method is adopted to construct map of N_mF₂, h_mF₂, and integrated Vertical TEC (VTEC) within height ranging from 110km to 750km with data derived form COSMIC radio occultation system. And global TEC maps in the Sun-fixed coordinate are also withdrawn from IGS GIMs. By comparing these maps, it can be found that N_mF₂, h_mF₂ and TEC increase in the morning hours and decrease in the afternoon and night. Under fixed location and local time bins, cases during SSW and non-SSW days from global COSMIC observations are compared, which shows that N_mF₂, h_mF₂, and VTEC during SSW days, on average, increase 17%, 12%, 10km in the morning , decrease 10%, 15%, 16km in the afternoon, and decrease 19%, 23%, 11km in the afternoon respectively. According to the results of comparison of IGS GIMs during SSW and no SSW days, the main difference occurs in the middle and low latitude region, moves along with UT time and corresponds to the position of ionospheric anomaly. It also can be found that increase of TEC (VTEC and IGS TEC) is stronger in the northern hemisphere than in the southern hemisphere during the morning time. Furthermore, the phenomenon that N_mF₂, h_mF₂ and TEC (VTEC and IGS TEC) are decreased in the night hours has never been mentioned by previous studies. So altimeter observations by the OSTM/JASON-2 satellite are used for further verification and the phenomenon is validated at last.