The main shaft bearing of a turboshaft engine adopts underrace lubrication structure.In order to verify the effectiveness of its oil collection and oil delivery structure,an experimental study on oil supply efficiency was carried out.The principle and scheme of the test were introduced,and the effects of speed,oil pressure and nozzle axial location on the efficiency were studied by experiments.The experimental results show that the oil supply efficiency is decreased with the increase of the oil pressure and the increase of the axial distance between the oil nozzle and the locking nut.The oil supply efficiency of underrace lubrication structure studied in this paper is more than 90%,which meets the design requirements under the engine’s typical rotation speed and oil pressure.