An electrically-actuated artificial muscle fiber with bidirectional linear strain and a preparation method thereof are provided. The artificial muscle fiber includes a fiber matrix, electrode layers and insulating layers. The artificial muscle fiber takes the fiber matrix as a skeleton, upper and lower layers of the fiber matrix are covered with one electrode layer respectively, and one insulating layer is covered on a surface of each of electrode layers. A helical fiber body is formed by winding. Finally, the artificial muscle fiber is formed through packaging, where metal wires are taken as leads and respectively connected to upper and lower layers of electrodes.