The utility model discloses a measuring device for measuring the thickness of the metal thin-strip. A metal thin-strip to be measured is placed between two Michelson interferometers, and two corresponding surfaces of the metal thin-strip to be measured respectively serve as a reflecting surface for each interferometer. The two Michelson interferometers are connected in series to form a differential interfering system. Through a first optical transmission system, a luminaire with low coherence degree is irradiated to the first Michelson interferometer whose output light is irradiated to the second Michelson interferometer by a second optical transmission system serving as a luminaire. Through a third optical transmission system, the output light of the second Michelson interferometer is received by an optoelectronic receiver and is processed by a signal processor to obtain the thickness of the measured metal thin-strip. The differentia measuring method of the utility model, having the advantages of high measuring sensitivity, vibration resistance, etc., is suitable for measuring the thickness of ultrathin-strip materials which are non-transparent and have relatively high optical reflectivity on both surfaces and have no base to support or no transparent base to support.