The invention discloses a nano-fiber yarn surgical suture and a preparation method thereof. The surgical suture is composed of a core layer and a shell layer, wherein the core layer refers to micron fiber yarns; and the shell layer is a tubular nanofiber membrane. The preparation method comprises the following steps: enabling multiple strands of micron fibers to penetrate through a metal funnel, and winding the fibers on a winding roller; preparing an electrostatic spinning solution from a biological material, rotating the metal funnel to twist the multiple strands of micron fibers into micronfiber yarns, spinning by using a double-needle electrostatic spinning system, and coating the surface of the micron fiber yarns with the nanofiber membrane so as to obtain nano-fiber yarns, and collecting the yarns by the winding roller. By utilizing a highly oriented nano-fiber structure in the yarns, adhesion, spread and proliferation of muscle fiber cells can be promoted, parallel nano-fiberson the surfaces of the nano-fiber yarns are favorable for growth of the muscle fiber cells, and wound healing is promoted.