Sea ice in polar areas is an important part of the global climate system. In order to obtain variations in sea ice extent for the Antarctic and Arctic, this paper analyzed the Special Sensor Microwave/Imager (SSM/I) sea ice data product dating from March 1, 1997 to December 31, 2006. During this period, the sea ice extent increased in the Antarctic with the trend of (0.5467±0.4933)×10⁴ km²·yr^–1, and decreased in the Arctic with the trend of (–7.6125±0.3503)×10⁴ km²·yr^–1. In different sectors of the Antarctic, variations of the sea ice extent are different. The sea ice extent increased in the Weddell Sea and Indian Ocean, but decreased in the Ross Sea, Western Pacific Ocean, and Bellingshausen/Amundsen Seas.