Abstract: The technology of PIV was creatively used in testing velocity field of helical flow of power-law fluid in eccentric annuli. A vertical annulus pipeline device was designed and its eccentricity was changed. Different density polyacrylamide solution of helical flow was tested in the vertical annulus pipeline with the application of PIV, and eccentricity degree of pipeline was 40% and 80%. Laws of axial velocity were obtained. When the pressure gradient was the same, axial velocity was increased by the decrement of viscidity and increment of the inner tube rotational speed. When the flow is the same, the velocity decrement in turbulent flow core area of wide gap was caused by the decrement of viscidity and increment of the inner tube rotational speed. Eccentricity increase may reduce axial velocity of the turbulent flow core area. When other conditions were the same, the axial velocity increased with the pressure gradient increase or the flow increase. The experimental results of PIV is in good accordance with the numerical simulation results of PHOENICS, so the method of testing the axial velocity field of helical flow of power-law fluid using PIV was feasible and effective.