Abstract: In order to investigate the influence of specific speed francis turbine on the internal flow regime changes and stability of the unit under partial load conditions in the hydro-photovoltaic-storage hybrid power generation system, the SST k-ω turbulence model was adopted for three large opening conditions of a domestic power station under rated head and maximum head conditions for steady and transient numerical calculation and the result of the unit was analyzed. The results show that the flow pattern inside the runner is stable under the partial load conditions, and turbulent flow areas appear at the runner outlet and in the lower annular flow passage. There is a cylindrical cavity vortex belt in the draft tube, which is derived from the runner discharge cone and develops in the straight cone section of the draft tube. The main frequency of pressure pulsation in the vaneless area of francis turbine under eccentric load condition is blade frequency, and the internal part of draft tube is mainly low frequency pulsation with similar amplitude. The research results reveal the changes of internal flow field, the development law of draft tube vortex belt and the causes of unit pressure pulsation of francis turbine in the hydro photovoltaic storage hybrid power generation system under the off load condition, providing constructive suggestions for widening the operation range of the turbine.