A sand source selecting structure for a sandblasting gun has a main body; a channel provided in the main body, for passing pressurized gas; at least two sub-channels provided in the main body respectively connected to the channel; a sandbox mounted on the main body connected to the channel through the first sub-channel; a first control valve installed in the first sub-channel; and a second control valve installed in the second sub-channel. Therefore, the combination of the first control valve with the second valve provides a selecting structure, which can offer different sand supply sources.