Under different relative inflow angles, this paper studies the control mechanism of off-surface small structure which is referred as micro-cylinder. With varying positions, the effect of micro-cylinder on reducing the flow separation on the horizontal axis wind turbine blade is investigated and the following results are found: (1) Under the condition of U-infinity = 13 mks, when it is closer to the blade tip, the relative inflow angle decreases gradually and tends to a stable range. The optimum micro-cylinder on each cross section gradually approaches to the blade leading edge with the decrease of relative inflow angle. (2) The optimal effect cannot been achieved when using the integrated micro-cylinder A which is formed by the optimal micro-cylinder segments on each cross section. Due to the complexity of flow field, the flow condition at each cross section could be influenced by the upper and lower parts of the flow field. (3) Under different stall conditions, setting a proper micro-cylinder in front of the blade leading edge can effectively suppress the flow separation on wind turbine blade without influencing the wind turbine stability. In this way, the aerodynamic performance of wind turbine can be improved effectively with the increase of power coefficient. (C) 2018 Elsevier Ltd. All rights reserved.