The invention relates to hyaluronic acid composite cross-linked hydrogel and a preparation method thereof. By combining the characteristic that an active group of hyaluronic acid can be used as a chemical modification site with the characteristic of polyanion electrolyte of hyaluronic acid, different groups and different spatial conformations of the substances such as 1,4-butanediol diglycidyl ether, polyethylene glycol, sodium alginate and gelatin are utilized to perform composite crosslinking and modifying with hyaluronic acid, and the proportion of each component is analyzed to determine the optimum formula of each component in the crosslinking reaction; the molecular weight of the prepared hyaluronic acid composite hydrogel is obviously increased, especially, the dynamic viscosity of the prepared hyaluronic acid composite hydrogel is remarkably increased. The hyaluronic acid composite cross-linked hydrogel prepared by the preparation method disclosed by the invention is great in molecular weight and great in dynamic viscosity, has the advantages of relatively strong space blocking effect and lubricating effect, good biocompatibility, good stability, and the like, and can be used for a tissue filling material, a lubricant in an articular cavity and a tissue adhesion preventing material of operation.