It is very important to select the appropriate type bucket for diversion and discharger tunnel at the export of particularly narrow valley.Based on the analysis of various bucket size and adaptation range,the paper proposed a Y type narrow slit.By aid of test data of discharge and diversion tunnel of a hydropower station, the paper studied the form of water tongue.The study found that after the discharger and diversion tunnel outlet used Y type narrow slit,the tunnel can not only form longitudinal pull water tongue in a variety of conditions and also satisfy the operation requirement of large working head amplitude change. The same bucket is used in diversion stage and permanent flood discharge without alteration.