The invention relates to a coaxial bidirectional filament spreading device of a beam-splitting filament and application. The filament spreading device is composed of a centering
yarn guide hook, a spreading disk for spreading the filament beam, a splitting separator, a filament spreading roller for spreading a splitting filament layer in a bidirectional way, a driving roller at the same speed as a front roller and the like, is connected to a
fixed frame and is mounted on a ring throstle through the
fixed frame. A method for spreading the beam-splitting filament coaxially and in the bidirectional way comprises the steps of: locating a filament on a
central line of a flat bottom groove of the spreading disk by the centering
yarn guide hook and winding on the spreading disk to finish the spreading of the filament beam; then splitting the filament symmetrically by the splitting separator to form two filament beam
layers with a certain interval, enabling the two filament beam
layers to enter into respective one-way filament spreading zones and respectively spreading the filament beam layer towards left and right under the action of a
screw thread groove to form a filament mesh; and outputting the filament mesh by surrounding and being close to a driving roller of the front roller. The filament spreading device can be applied to
spinning of protective type soft, smooth, high-count composite yarns and superfine branches of fibers which are ultra-short, easy to drop scraps and easy to generate flying and shorter and weaker fibers.