The East Asian monsoon (EAM) has been experiencing a considerable decadal weakening since around the end of 1970s with a significant southward shift of increased precipitation in East Asia.Such a decadal change has caused serious consequences by increasing drought and/or flooding and altering water resource distribution, which can affect the sustainable development in East Asian region.However, the reason for the decadal change in EAM remains unclear.This talk will present our current understandings on this issue.