Abstract: When tachogenerator malfunctioned, abnormal signal (voltage lower) would overspeed the machine and damage the mechanical linkage in the automatic speed control system in GDX1, GDX2 packing machines.GD0S-1 type GD direct-current motor overspeed alarming and protecting system was developed, its principle and control process were discussed in detail.This system could effectively avoid overspeed, reduce maintenance and improve production efficiency.