Abstract: In this study, a flume experiment was conducted on free surface air-core vortices and the data was measured using Particle Image Velocimetry (PIV). Tangential velocity distributions, circulation distributions and water surface profiles of the vortices have been obtained. Based on these experimental data and theoretical analysis, we developed a mathematical model that describes the vortex characteristics including the equations for tangential velocity distributions and water surface profiles. Comparison with previous mathematical models shows that our model agrees with the experimental data better, and it gives a maximum tangential velocity of that is close to the measurements. The formulae presented in this paper can predict the same tendency of smooth and continuous variations as shown by our measurements. The results would help solve the vortex problems in the research and engineering application of hydraulic intakes.