The phase Ⅲ RCC cofferdam construction belongs to the phase Ⅲ diversion works. It is a key item to ensure achievement of the reservoir impoundment, navigation and power generation in 2003 and the guarantee to the safety construction of the follow-up right-bank intake dam section and the powerhouse. Restrained by navigation while construction, the construction site and duration, both the concreting intensity and the rise height of the phase Ⅲ RCC cofferdam exceed the current construction level. In view of these difficulties, a huge amount of research work has been performed by relevant departments and is described in the paper.