A method using Michelson interferometer, polarization interferometry system and white-light vertical scanning system for measuring the retardation of wave plates (including the order of retardation) is presented. Two beams with the same polarization directions are introduced after a collimated white-light passes through the polarization interference system. Then the two beams are respectively reflected by two plane mirrors of the Michelson interferometer. As the moving mirror driven with piezoelectric transducer (PZT) scans vertically, three white-light interference packets are formed and are captured by a CCD camera. The retardation of wave plates can be calculated by the optical-path difference between the central packet and side packet. A multiple-order wave plate is tested by the white-light interference vertical scanning method, and the measured retardation (4268.1 nm) coincides with the that (4269.9 nm) measured by spectroscopic scanning method.