As one of the main diseases of ancient murals, soot pollution has seriously affected their artistic value and visual appearance. In view of the soot diseases of grotto and temple murals, we prepared mildly, moderately and heavily sooted test blocks using simulation techniques, and conducted soot-cleaning experiments with Carbomer gel, agar gel and gellan gum. The morphology, cementation state and cleaning efficiency of soot stains were analyzed using microscopic observation, profile analysis and Fourier transform infrared (FTIR) spectrometry. The results show that the three kinds of gel materials had better cleaning effects on mildly and moderately sooted test blocks and could relieve heavy soot to certain degrees, turning dark brown pollution into light grey. Among the three, Carbomer gel has the best cleaning effect. After observing interfaces with a portable microscope, we found that 1) black and brown stain particles were densely distributed in the uncleaned area, and that stain particles in the cleaned area were greatly reduced; 2) in contrast, after cleaning, small amounts of stain particles and pigment particles were alternately distributed in the uncoated murals, and the coated murals were free of stains except for only a few small brown bubble structures on the surface of the heavily sooted test blocks (the natural colors of pigments can be completely recovered, and the brightness of murals can be greatly improved). In addition, there was no gel residue on the wall paintings according to FTIR analysis. However, the soot-cleaning effect is affected by many coupling factors, such as whether a mural has a coating, degrees of aging, concurrent vulnerability to diseases, types of soot or burning, degrees of combination between soot stains and mural pigments, and differences between fuel media that lead to sooting. At present, cleaning with gel is only suitable for soot of coated murals and non-heavy soot of uncoated murals. This study may provide a reference for the cleaning of soot diseases of ancient murals.