Abstract: In order to study the internal flow characteristics of bulb tubular turbine under low flow condition,taking the tubular turbine of a hydropower station as the research object,the RNG k-ε turbulence model is used for numerical calculation,the draft tube efficiency of draft tube and the flow in the whole channel under the condition of low flow are analyzed,and the pressure pulsation of hydraulic turbine flow parts is analyzed quantitatively.The analysis shows that when the head and guide vane opening not match under the condition of low flow,the draft tube efficiency is reduced,the change trend of draft tube efficiency is related to unit efficiency,when the draft tube efficiency decreases by 2%-3%,the unit efficiency will decrease by 1%. Interaction between the main flow area of the runner and the water flow Static area of the draft tube,vortex structure is formed on the side wall of draft tube,there is obvious backflow in the draft tube and high-speed fluid exists in the side wall.Pressure fluctuation is more prominent under low flow conditions,mainly affected by low frequency pressure fluctuation,the main frequency at the inlet of the runner comes from the circulation of the unit provided by the guide vane,which is close to the blade frequency of the runner.In the draft tube,it is mainly affected by low frequency pressure fluctuation with 0.2 Hz,the pressure fluctuation coefficient increases along the draft tube,the maximum pressure fluctuation coefficient is 1.75%.