Fading phenomenon under natural environment is complicated. Strictly, it is impossible to reproduce above phenomenon. However, it is possible to reveal a reasonable mechanism for fading ancient mural, and the rationality proposed mechanism could be verified by experimental method, which is a basic point of view of natural science. In this paper, the viewpoint that the fading of mural painting caused by degradation of binder rather than change of pigments, was proposed. To verify this viewpoint, the following experiments were conducted. To construct the simulated mural painting with stable pigments and degradable binder, thermally stable ocher and thermally degradation gelatin were used in preparation of simulated mural painting. The composition and surface of simulated painting before and after calcination were characterized by TG, IR, SEM and reflectance spectroscopy, respectively. The following results were obtained. After calcination, pore structure emerged in painting layer. From multiple-angled reflectance spectra, the reflectance of visible light increased and the absorption decreased, and the color fading of the simulated sample was observed. The ionic liquid, colorless, nonvolatile and no reaction with painting layer, was coated on the surface of faded sample. Taking the same characterization method to investigate the surface morphology and optical properties changes before and after ionic liquid treatment, the results indicate that the pore in faded painting layer was filled by ionic liquid. Furthermore, reflectance for treated painting layer decreased, the absorption improved and the color of faded painting layer changed to deep color. In fact, this experiment result could verify the conjecture that morphology changes in painting layer could cause the fading. According to this results, a real faded ancient mural painting was restored using the same method and the restoration is remarkable.