Wetland is an ecosystem formed by the interaction of land and water, whose size is highly susceptible to climate change and human activities. In this report,we sampled Baiyangdian wetland,the largest natural lake wetland in the North China,by extracting and analyzing wetland information from the eleven remote sensing images during 1984-2013. Thirteen parameters derived from the climate,economic,population and agricultural aspects were evaluated by principal component analysis and the major driving forces affecting the wetland size were determined. The results revealed that the wetland size increased first and then decreased, followed by a slow and gradual increase with an overall descendent trend. The total area of Baiyangdian wetland was on average 25008 hm~2 during 1984-1997 and 21573 hm~2 during 1998-2013. Social and economic development, agricultural development and precipitation reduction were major driving factors, and social and economic developments were the most significant contributing factor. To curb the decreasing trend of the wetland size,we should effectively control the use of upstream water,improve water use efficiency, and essentially reduce the pressure of human activities on the wetland,thus naturally increasing water input in the wetland.