The rapid increase of sludge has brought significant environmental problems, the solar drying is an effective and economical method for sludge reduction. However, single solar drying has key issues such as low efficiency and long time. Thus, an interesting activated carbon synergistic solar (ACSS) technology which dried municipal sludge with was innovatively proposed in this paper. The changes of sludge pore structure were characterized by fractal dimension and scanning electron microscope, and surface elements were detected and analyzed. The reflectance and light transmittance were determined by UV-VIS-NIR to obtain the light absorptivity. The effect of key parameters including sludge thickness, light intensity and activated carbon content on drying rate (D