Ancient Qigu bronze mirrors are known for their dense and smooth surface. However, due to burial and storage environments, their surfaces are often covered with corrosion products, soil, and other deposits, which compromise both their appearance and long-term preservation. Traditional cleaning methods for the surface layer of Qigu can easily cause scratches and allow chemical reagent to penetrate the surface. In this study, we investigated the corrosion characteristics of a black Qigu bronze mirror from the Tang Dynasty and, and following the principle of “minimal intervention” in cultural relic conservation, we designed and prepared a novel composite hydrogel cleaning material to clean the black Qigu bronze mirror. First, we examined the black Qigu bronze mirror and its surface attachments. X-ray fluorescence (XRF) spectrometry revealed that the mirror was made of high-tin bronze. Microscopic observation showed distinct grinding marks, dense pores, and cracks in the black Qigu regions. The corroded areas exhibited layered accumulations of hardened deposits. Scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) showed that the hardened deposits consisted mainly of soil and copper corrosion products. Further analysis using X-ray diffraction (XRD) indicated that the primary components of the corrosion products were malachite and quartz.  We then conducted experiments to prepare and optimize composite hydrogel materials. Carboxylated chitosan, known for its water solubility, antibacterial properties and metal ion adsorption capacity, was cross-linked with carbomer, a thickening agent, through electrostatic interactions to form a gel carrier. Formic acid was selected as the active corrosion-removing component. By directly mixing these reactants at room temperature, we prepared a series of gel agents with different concentrations. The optimal concentration of the system was determined through viscosity test and simulated sample experiments, resulting in a white, glossy semi-solid gel cleanser with an average viscosity of approximately 82 000 mPa·s. SEM observation revealed a honeycomb-like porous structure in the gel’s microscopic morphology. Finally, the prepared composite hydrogel cleanser was applied to remove corrosion from the black Qigu bronze mirror. The mirror surface was largely covered with hardened corrosion, aged labels and other contaminants. The gel cleanser not only reacted with the corrosion but also adhered to and removed other contaminants. The procedure involved repeatedly applying the gel cleanser to the corroded areas, with each application lasting 30 min. After treatment, the gel was dried with a hair dryer, allowing it to be peeled off. Microscopic observation, ultraviolet light examination, and scanning electron microscopy confirmed that the gel cleaning effect was significant and left no residue. This research focuses on the cleaning of corrosion on Qigu bronze mirrors. Compared with previous studies , it presents two key innovations:1) addressing to the limitations of the traditional cleaning methods for Qigu bronze mirrors, it applied a hydrogel cleaning approach to the conservation and restoration of high-tin bronze artifacts, and further evaluated both the cleaning effectiveness and the potential gel residues of the cleanser, providing a valuable reference for the conservation of similar cultural relics; 2) it designed and prepared a carboxylated chitosan/carbomer composite hydrogel system specifically for the conservation of bronzes, offering a new approach for the application of the composite hydrogels in cultural relic conservation.