The invention discloses a yarn feeder. The yarn feeder comprises a tension sensor, a motor and an electronic control unit, and is characterized by comprising a spindle-shaped body with corners adopting fillet transition; the motor is arranged in the middle of the body; a roller driven by a motor synchronously is arranged on the front surface of the motor; the center of the roller is positioned in a center line; the tension sensor is arranged at the lower part of the body; the electronic control unit comprises a control panel mounted inside the body, receives tension signals fed back by the tension sensor and adjusts the starting and stopping rotate speed of the motor. The yarn feeder has obvious effects of being simple and reasonable in structural design, and beneficial to keeping of the stable output of yarn tension.