Abstract: Steel bifurcations with inner crescent rib are widely used in the penstocks embe d ded in rock because of the advantages of less water head loss,good bearing condi tion,smooth outline and less excavation dimensions.However,it is very unpopular for this kind of bifurcation to be laid above the ground surface,especially in t he case of large diameter and high water head. Through an illustration of the st eel bifurcation of some hydroeletric project,the optimization of its configurati on are carried out by using finite element analysis under the condition of satis fying the requirement of water flow and structural loadcarrying capacity and some conclusions are obtained.