The invention relates to a multilevel waste heat quenching system, in particular to an online multilevel waste heat quenching system capable of weakening the quenching residual stress of an extruded profile, which belongs to the field of the high-temperature deformation heat treatment of metal. The multilevel waste heat quenching system comprises a guide passage which is arranged in front of an outlet of an extruder and has a spraying function, wherein the guide passage sequentially consists of an air injection guide passage and a water injection guide passage or sequentially consists of an air injection guide passage, a mist spraying guide passage and a water injection guide passage. On the basis that the time effectiveness enhancing effect is guaranteed, the quenching residual stress of the extruded profile is weakened, the core fracturing is avoided, the prestretching difficulty is alleviated, and the stability in shape and size of a final product can be realized.