The invention belongs to the technical field of a packaging material, and more specifically relates to a PE fresh-keeping coating membrane preparation method and a purpose thereof. The method takes mulberry fiber as a biomass raw material to prepare the rod-shaped nano bio-particles, carboxymethyl chitosan is taken as an antiseptic to prepare modified polyvinyl alcohol coating liquid, and then a PE base material is coated to prepare the coating membrane having fresh-keeping and corrosion resisting performances. Compared with traditional TiO2 and SiO2 inorganic nanoparticles modification, the rod-shaped nano bio-particles and polyvinyl alcohol have good compatibility, and the prepared fresh-keeping coating membrane has excellent obstructing performance.