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The limitation of traditional measurement technology in gas-liquid two-phase flow measurement is broken through.The liquid velocity field and vortex rope morphology from two vertical directions were measured synchronically by using particle image velocimetry and pulsed shadowgraphy technique. Experimental measurements show that the vortex rope in the draft tube presents three kinds of unstable circulation flow evolution, single spiral, double spiral, and overstocked rupture. When a single spiral vortex rope is partially split into two, it becomes a double spiral vortex rope. When the local spiral rise angle of a single spiral vortex rope decreases, it becomes an overstocked rupture. When there is a single spiral vortex rope in the draft tube, the vortex rope rotates precession around the central axis along with the liquid main flow, and the flow is divided into two parts, the outer main flow zone and the central stagnation zone, according to the axial velocity. The shear layer between the main flow zone and the stagnation zone rolls up to form several vortices. The position of liquid vortices determines the spatial morphology of the spiral vortex rope.