Abstract: An automatic coil-loosening-preventing system is developed to fix the problem of coil-loosening as encountered with during the uncoiling operation step of the spiral welded pipe mill line, and caused due to such an improper operation that the press-down of the conical head is not adjusted in time.Elaborated here in the essay are the main aspects of the said control system, including the operating principle, derivation and calculation of the major parameters, and the protective measures against over pressing by the conical wheel.The actual effectiveness of coil-loosening prevention by the said control system is demonstrated.The operation result shows that the system is capable of consistent and reliable running, satisfactory control effectiveness, and reducing the coil-loosening incidence by 80%, being worthy using as a reference for modifying the control systems of similar operation lines.