Abstract: The long-term operation of the turbine in the low load area will lead to large vibration and poor flow pattern of the hydropower unit,which will lead to cracks in the runner blades and cavitation of the unit. In order to explore the flow characteristics and pressure pulsation characteristics in different parts of the unit,this paper makes a three-dimensional modeling of a mixed flow hydropower unit in a power station,based on Reynolds time averaged N-S equation and standard SST k-ω Based on the turbulence model,the steady and unsteady solutions are calculated for the rated working condition and partial load working condition（45% rated working condition）. The results show that the flow in the guide vane is more turbulent under low load conditions,mainly because the opening of the guide vane does not allow the water to enter the runner fully,and the pressure change near the crown of the runner is chaotic and does not decrease according to the law,and the energy conversion is low,resulting in lower efficiency. From the pressure pulsation results can be seen:the maximum amplitude at the movable guide vane is more than 3 times the maximum amplitude at the fixed guide vane,indicating that the closer the runner,the more obvious the effect of static and dynamic interference;the maximum amplitude inside the runner is several times the maximum amplitude at the guide vanes;the amplitude of pressure pulsation under low load conditions is mostly much higher than the maximum amplitude under rated conditions,indicating that the stability under low load conditions is poor. The results of this paper provide a certain theoretical basis for setting the safe operating range of mixed-flow turbine unit at low load.