The invention provides a fan comprising an air duct, a motor, a flow guide piece and an impeller assembly. The motor is arranged in the air duct; the impeller assembly is arranged at a first end in the axial direction of the motor; the flow guide piece is arranged in the air duct and positioned at the second end in the axial direction of the motor, and the cross sectional area of the outer surfaceof the flow guide piece gradually increases towards the direction close to the first end of the motor; and according to the fan provided by the invention, the wind resistance and the noise can be effectively reduced, and the air inlet and outlet quantity can be stably improved.