An experimental investigation of effects of a kind of streamwise-grooved blade on the unsteady flow field at an exit of an axial-flow fan was performed.The flow field at 25% chord downstream from the trailing edge at hub was measured using a fast-response five-hole pressure probe at different mass-flow conditions.The unsteady flow of the grooved blades was compared with that of the smooth blades.The measurement results indicate that: (1) the grooved blades restrain the velocity fluctuation and the pressure fluctuation by modulating the blade boundary layers,which contributes to the flow loss reduction in the hub region and in the rotor wake region at the design condition;(2) the stream-wise grooves play an important role in restraining the radial migration in the blade boundary layer and abating the tip flow mixing,which contributes to the flow loss reduction in the tip region at the design condition;(3) at the near stall condition,the grooved surface can not reduce the flow loss,even in- crease the loss nearby when the separation happens in the blade boundary layer. An experimental investigation of effects of a kind of streamwise-grooved blade on the unsteady flow field at an exit of an axial-flow fan was performed. The flow field at 25% chord downstream from the trailing edge at hub was measured using a fast- response five-hole pressure probe at different mass-flow conditions. the unsteady flow of the grooved blades was compared with that of the smooth blades. the measurement results indicate that: (1) the grooved blades restrain the velocity fluctuation and the pressure fluctuation by modulating the blade boundary layers, which contributes to the flow loss reduction in the hub region and in the rotor wake region at the design condition; (2) the stream-wise grooves play an important role in restraining the radial migration in the blade boundary layer and abating the tip flow mixing, which contributes to the flow loss reduction in the tip region at the design condition; (3) at the near stall condition, the grooved surface can not reduce the flow loss, even in crease the loss nearby when the separation happens in the blade boundary layer.