Abstract: Cavitation is a special unstable hydraulic phenomenon in the process of fluid energy conversion. Cavitation phenomenon can even lead to heavy losses of hydraulic machinery overcurrent components due to cavitation erosion damage in extreme cases. In order to explore the relationship between the cavitation phenomenon and vortex in Francis turbine under different load conditions. The numerical calculation of three-dimensional cavitation flow in the whole passage is thusly carried out for the francis turbine under different load conditions. The results show that: The cavitation in Francis turbine mainly exists in the runner and draft tube basins with more complex flow characteristics, and the intensity of cavitation increases with the decrease of unit load; and compared with the rated condition, the peak cavitation volume in the runner basin increases by about 32 times in the minimum load condition; Under 104% overload condition and rated condition, the shape of the vortex rope in the draft tube is an axial straight vortex structure, namely spindle vortex rope; the unit load is reduced to 93% and 80%, the vortex rope in the draft tube dominates the flow characteristics of the draft tube basin; due to the "squeezing" effect of the vortex rope structure on the surrounding fluid and the action of eccentric helical motion, the axial symmetry of the flow state is broken, so that the strength and position of the fluid in the high-speed region around the vortex core also change with the change of the vortex rope in the time domain, cavitation occurs in the vortex core, and the type of vortex rope evolves into cavity spiral vortex rope; The load of the unit continues to decrease and the implicated velocity component of the circumferential rotation of the fluid in the draft tube gradually becomes extremely dominant; due to insufficient flow in the draft tube, the vortex rope shape of the draft tube is difficult to maintain a stable operation; under 64% and 47% load conditions, the huge cavity squeezes the draft tube space and compresses the wall fluid, and the vortex rope structure is broken to form the cavity wrung vortex belt; Under partial flow conditions, the cavitation volume fluctuation in the draft tube presents a low-frequency fluctuation with a frequency of 0.075~0.225 times the runner frequency, and its fluctuation frequency decreases with the load reduction; and the fluctuation of the cavitation volume in the draft tube may induce the low-frequency pressure fluctuation on the draft tube wall.