Abstract: Due to long term water retaining, the overhaul gate of release tunnel of a hydropower station can not be closed in emergency and needs to be reconstructed. In the view of reducing investment, we adopt a united plugging system composed of concrete blockage, pre-buried penstock, steel blocking head and manhole. In the system, the force structure of the concrete blockage, penstock and steel blocking head are definite and the stress could be calculated respectively. The manhole set on the steel blocking head would produce significant local stress and becomes a weak point, so three dimensional finite element analysis is needed in the calculation. The design details for various parts of the united plugging system are introduced, which could provide reference for the similar plugging project.