The present invention provides a hydrogel platform using, as a substrate, hyaluronic acid (HA) conjugated to a pyrogallol (PG) moiety. The HA-PG conjugate of the present invention can be rapidly crosslinked by two different methods, in each of which an oxidizing agent is used or a pH is adjusted. The hydrogel of the present invention can not only have excellent biocompatibility, but also can have efficiently controlled physical characteristics such as a crosslinking rate, elasticity, and adhesive strength, depending on each crosslinking method. On the basis of such excellent stability and functionality, the hydrogel of the present invention can be used in various fields including drug delivery, biopharmaceutical materials such as a wound healing agent or anti-adhesive agent, medicines, and cosmetic products.