he Baiyangdian Lake is the largest freshwater lake and an important aquatic ecological function region in north China.Under the natural and artificial influences, its ecosystems has being obviously degraded. This paper discussed the ecosystem degradation and its driving mechanism based on the evolution of the ecohydrological process in the Baiyangdian Lake basin. The climate aridity is the natural background of the ecosystem degradation, but upstream water interception,hydraulic engineering and the utilization of water resources are the inducing factors to accelerate the wetland degradation. Finally comprehensively considering the present state of ecosystem degradation and its driving mechanisms, measures and proposals are put forward to protect the Baiyangdian Lake from the perspective of ecohydrology.