The invention provides a device for spreading large-tow carbon fibers through combination of a sound wave method and a mechanical multi-roller method. The device for spreading the large-tow carbon fibers comprises a yarn containing device used for containing a fiber tow. The device for spreading the large-tow carbon fibers is characterized in that after being guided out of the yarn containing device, the fiber tow enters a tension control device, the surface tension of the fiber tow is controlled by the tension control device, the tension is kept constant, the fiber tow with the adjusted tension passes through the space between a pressure feeding roller and a second supporting roller and then is guided into a yarn pre-spreading device, the fiber tow is pre-spread by the yarn pre-spreading device according to the sound wave method, the pre-spread fiber tow is guided into the main yarn spreading device, the fiber tow is spread through the mechanical multi-roller fiber expanding method by the main yarn spreading device, and the spread fiber tow is rolled through a traction take-up device. The device for spreading the large-tow carbon fibers can effectively and fully spread the large-tow carbon fibers.