The invention belongs to the technical field of electrochromic devices, and discloses a functional hydrogel-based electrochromic device and a preparation method thereof. The method comprises the following steps: using acrylamide as a monomer, N,N-dimethylbisacrylamide as a cross-linking agent, ammonium persulfate as a thermal initiator, 4-hydroxy-2,2,6,6-tetramethylpiperidine oxide as a catalyst to prepare polyacrylamide hydrogel; adding a solution having electrolyte, electro-alkali, and base-responsive molecules to the hydrogel at room temperature, and adsorbing the solution by the swelling action of the hydrogel to obtain a functionalized hydrogel; and sandwiching the hydrogel between two ITO glass electrodes to obtain a functional hydrogel-based electrochromic device. The functional hydrogel-based electrochromic device and the preparation method thereof are simple in preparation process, mild in working condition, use water as a solvent to reduce the harm to the human body, which isenvironmentally friendly, good in reproducibility, and very suitable for industrial production.