The invention relates to the field of paper-plastic combination, and particularly discloses a paper-plastic combined packaging bag and a preparation method thereof. The paper-plastic combined packaging bag is prepared by the steps of mixing low-density polyethylene, phenolic resin, filler, turpentine, vinyltrimethoxysilane, tritolyl phosphate and a silane coupling agent with a mark KH570 to prepare colloidal particles; adding the colloidal particles into an extruder, carrying out extrusion molding and processing to prepare a packaging bag for paper-plastic combination; and heating the packaging bag for paper-plastic combination, coating the surface of kraft paper with the packaging bag to for a plastic layer, and molding to form the paper-plastic combined packaging bag, wherein the filleris prepared from bark, herbaceous plants, chitosan, chitin fiber, diatomite, calcium stearate, sodium alginate, hydrotalcite, iron stearate and yttrium. According to the packaging bag, raw materials are rich in source and are easily available, and the packaging bag has excellent degradation performance, is durable and environmentally friendly and is suitable for being widely used.