With climate change occurrence,such as global warming,polar sea ice has been drawn increasing attentions. Synthetic aperture radar (SAR) can monitor earth independent on sunlight and cloud. GaoFen-3 is a C-band SAR of the GaoFen series satellites,which has multiple imaging modes and can obtain data globally. SAR plays an important role in monitoring polar sea ice due to the advantage of all-weather operation and high spatial resolution. Bases on the GaoFen-3 horizontal-vertical data,we proposed an automatic method to discriminate sea ice and sea water, using the support vector machine classification method. The detected sea ice shows good agreement with visual inspection. The successful development of this algorithm supports the Gaofen-3 SAR for operational service of monitoring polar sea ice.