The present invention relates to a polyvinyl alcohol hydrogel having an asymmetric pore size. the pore size of the upper surface of the polyvinyl alcohol hydrogel is 1-30 μm, the pore size of lower surface thereof is 50-300 μm, and the pore size of the hydrogel gradually increases from the upper surface to the lower surface. The polyvinyl alcohol hydrogel in the present invention has excellent biocompatibility, and has functions of blocking bacteria, anti-adhesion, the absorption of exudate, promoting wound healing, observing in situ of wound healing process and the like.