The nonlinear circulation mathematical model of axial flow pump impeller was established based on the independence assumption of the cylindrical layer, the velocity gradient equation and meridional velocity equation in axial-flow impeller outlet. Miniature five-hole spherical probe was used to measure circulation and meridional velocity of South-to-North Water Diversion Project axial flow pump model (TJ04—ZL—06) in the blade outlet at the optimal condition. The experimental results show that the nonlinear circulation distribution appears in the axial flow impeller outlet. The circulation curve is relatively flat in the central of blade, while it reduces to about 0.8 times near hub and increases to about 1.2 times near tip. The meridional velocity distribution shows parabolic flow pattern and the maximum velocity appears in the middle of blade. The meridional velocity in blade outlet was calculated based on nonlinear circulation mathematical model. The results show that the calculated values show agreement with the experimental results, and the calculation errors of different radius points are less than 5%.