White Light Interferometry (WLI), overcoming the disadvantage of the phase ambiguity in the narrow-band interferometry, allowed absolute position determination. A new tandem differential white light interference system for the thickness measurement of metallic foil was designed. In this work, the differential white light system consists of two Michelson Interferometers (MI) in tandem. Reflective surfaces measured were the corresponding surfaces of metallic foil. Therefore, the measured result is only related to the thickness but not to the position of metal foil. Theoretical analysis and preliminary experimental results show that the method has advantages of high accuracy, fast detection and anti-interference.