Abstract: Depending on the 1/so large scale physical model of flush galleries of Dachaoshan hydropower station,type optimization tests of forward direction,reverse direction and bidirectional flush galleries were carried out.On the part of sand escaping effect, hydraulic character and wear strength etc.,the general layout,opening elevation, dimension and the setting standard of the diversion angle of flush galleries are discussed. Finally,optimized bidirectional flush galleries adequate and acceptable to design department are proposed.