The invention relates to the technical field of wire and cable processing, and discloses a straightening device for a large-diameter cable. The straightening device comprises a machine frame. The machine frame is sequentially provided with a first straightening mechanism, a second straightening mechanism, a third straightening mechanism and a fourth straightening mechanism which are used for straightening the cable. The first straightening mechanism is arranged to be a straightening box with a cone through hole. A bend detection mechanism is arranged at a cable exit of the straightening box. The second straightening mechanism comprises a motor and two sets of airflow straightening equipment which are driven by the motor and are symmetrically arranged at the machine frame. Four times of straightening effect can be gradually conducted by the first, second, third and fourth straightening mechanisms. Straightening can be achieved during the travelling process of the cable, and cable damagecaused by forced straightening in the prior art can be avoided.