A series thermoreversible hydrogel CS-Ag were prepared by the supermolecule complexation of chitosan with silver ion. The CS-Ag systems are in the semi-transparent and stable flowable sol state at room temperature, and become the gel state at temperature above 50 °C in 2 min and recover to flowable sol state when temperature was below 50 °C. This phase transition process could be repeated at least 5 times and shows a good stability. The structure and chemical state of the hydrogel were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and X-ray energy spectrometer (EDS). The thermoreversible hydrogel CS-Ag with same gelation temperature could be prepared by adjusting the AgNO3 amount and the pH value simultaneously. The different supramolecular interactions of the -NH2 group of chitosan in the hydrogel system at different temperatures were proposed to dominate the reversible thermo-responsive process of CS-Ag hydrogel. CS-Ag-19 hydrogel showed good antibacterial, and injectable and thermos-gelation performance, and it had potential application as hydrogel antibacterial dressing.