A yarn feeder may comprise a driver and a winding wheel. The driver has a front cover, a rear cover, a stator disc and a rotor disc, and the front cover and the rear cover are configured to fit together to form a housing therebetween which accommodates the stator disc and the rotor disc therein. The stator disc has a first through hole, and a plurality of teeth are formed around the first through hole to enable a couple of coils to be wound thereon. The rotor disc has a connecting hole, and a plurality of magnetic members are formed around the connecting hole. A connecting base extended from a first end of the winding wheel is engaged with the connecting hole, and the driver is connected to a tension controller to detect the tension of yarn and further to control the rotational speed of the driver.