The invention relates to a medical hydrogel dressings and a preparation method thereof. The hydrogel dressings is prepared by taking 10-30% by mass of starch and 2-15% by mass of water-soluble polymer as raw materials, utilizing a guanidinesalt polycondensate as an anti-bacterial agent, adding a cross-linking agent, and reacting at the temperature of 40-80 DEG C. The operation steps are as follows: adding the starch and the water-soluble polymer in a solvent to prepare into a solution, regulating the pH value of the solution by a NaOH solution, heating for gelatinization, cooling, adding the anti-bacterial agent and the cross-linking agent, stirring to form a mixed solution, pouring the mixed solution into a die, and reacting at the temperature of 40-80 DEG C to obtain the anti-bacterial hydrogel. Compared with the prior art, the hydrogel dressings in the invention has the advantages of good swelling property, high transparency, moderate mechanic strength, excellent bacteria invasion resistance, wide raw material sources, cheap raw materials, good tissue compatibility and favorable medical application prospect, and can effectively prevent wound infection.