The invention discloses a slag waste heat recycling system. The system sequentially comprises a slag mixing device, a main transferring device, a material collection hopper, a cooling device and a cold slag collecting device from left to right. The material collection hopper is provided with a breaking device, and a material pushing device is arranged on the cooling device; a feeding end is arranged at the left end of the material pushing device, and a discharging end is arranged at the right end of the material pushing device; meanwhile, the cooling device is located inside an insulation chamber, and at least two waste heat recycling openings are arranged on the top of the insulation chamber in sequence from left to right; the left portion of the main transferring device is matched with the slag mixing device, and the material collection hopper is located below the right end of the main transferring device; and the material collection hopper is located above the feeding end, and the cold slag collecting device is located below the discharging end. The slag waste heat recycling system has the beneficial effects that high-temperature slag can be treated relatively thoroughly, and the waste heat recycling efficiency is higher; and the invention further discloses a slag waste heat recycling method.