Abstract: A mixture cavitation model for francis turbine internal flow was developed, and the numerical calculation was carried out.As a result, the internal flow characteristics of high flow condition, the optimal flow conditions and low flow condition turbine were obtained.The results showed that in the high flow conditions and low flow conditions, the low pressure area of the draft tube center section corresponded to the vortex.The amplitude of the pressure fluctuation was mainly affected by the pressure difference of the draft tube vortex diameter ends.There was large whirlpool area at the ends of the tube inlet sides and near the elbow segment.It caused larger energy dissipation and reflow phenomenon in the draft tube and disorder in the turbine flow.