Abstract: An amplifier which is used to measure the static and dynamic speed droop has been developed successfully, it gives out higher sensitivity and responsibility.It is proved by the experimental data that the speed grade of the D.D.D system can meet the requiremenets of the continuous rolling technique.The advantage of D.D.D continuous rolling technique is that the skill is simple enough to be masterd, the investment in building is little and that the speed of building is faster, It can be used as one of the plan in rebuilding the bar mill in our country.