Polylactic acid filament and preparation method thereof

The invention provides a polylactic acid filament and a preparation method thereof. The preparation method comprises the following steps: extruding and melting dried polylactic acid slices and optional color master batches by using a screw extruder to form a melt; the melt is filtered and sprayed through a spinning assembly in a spinning manifold, and melt filaments are formed; cooling and molding the melt filaments by using a circular blowing device, and extracting monomers and oligomers by using a monomer suction device to form nascent fibers; oiling the nascent fibers, and then carrying out network treatment to obtain pre-oriented polylactic acid filaments; or oiling the nascent fiber, and then sequentially carrying out network treatment and drafting heat setting to obtain the fully-stretched polylactic acid filament. The polylactic acid filament provided by the invention has the advantages of low linear density deviation, high breaking strength, high evenness unevenness and low boiling water shrinkage, an