This study investigated the flow characteristics of a Horizontal Axis Wind Turbine (HAWT) rotor surface during rotation with wind tunnel experiments. Firstly, the effect of Laser Doppler Velocimetry (LDV) system on the power coefficient of HAWT was measured. Then, the flow distributions near the blade surface were measured at the different radial positions (r/R = 0.3 and 0.7) in the cases of the low and optimal tip speed ratios. At last, the radial position effect on the flow field features in boundary layer were also investigated in detail. As a result, the boundary layer thickness decreased at the blade leading edge and then increased rapidly along the blade surface at the trailing edge region. Furthermore, in the case of r/R = 0.7, the two-dimensional resultant velocity in the acceleration region of boundary layer showed smaller value than that of r/R = 0.3. Meanwhile, the flow in the blade root showed a large expansion of the deceleration zone at the low tip speed ratio. The results acquired from this study was suitable for designing the airfoil and had a better understanding of the radial position effect on dynamic stall. (C) 2019 Elsevier Ltd. All rights reserved.