Abstract: In order to measure the vortex flow filed in the components of fuel assembly, spallation target and heat exchanger for Generation-Ⅳ nuclear reactors, the vortex flow field was measured in an agitation facility driven by four-straight impeller through ultrasonic Doppler velocimetry (UDV) method. The two-dimensional vortex flow mapping in vertical section was acquired, which was based on vector synthesis in radial direction and axial direction. The results indicate that the flow velocity increases with Reynolds number. Of two large vortexes, one occurs in the upper fluid domain with counterclockwise direction, and the other below with clockwise direction, exists on both sides of the impeller. In addition, the large velocity gradient exists and the turbulence intensity increases with Reynolds number. The velocity in the depth of impeller is great while it is very small on both upper and down sides of the impeller. It greatly illustrates the variation characteristics of the vortex flow filed, and the UDV method can be used for measurement of complicated flow field.