Morphology is a crucial factor in determining the chemical, optical, and electrical properties of nanoscale materials. In this work, we utilized a facile room-temperature deposition method to synthesize three-dimensional (3D) coral-like Ag2S nanostructures. The formation mechanism of 3D coral-like Ag2S nanostructures was proposed by tracking the reaction process. In comparison with 0D Ag2S nanoparticles and 1D Ag2S nanowires of similar size, 3D coral-like Ag2S nanostructures exhibit higher pore volume, photocatalytic activity and cyclic stability for degradation of methyl orange (MO). Surface photovoltage measurement, electrochemical impedance spectroscopy, and Mott-Schottky analysis showed that compared to other Ag2S nanostructures, 3D coral-like Ag2S nanostructures have the strongest surface photovoltaic response, longest carrier lifetime, and highest carrier density.