In this paper, a dual-beam normal incidence polarization interferometer is presented to measure the flying height or head-disk spacing. It has the advantages of both the intensity interferometry method and the oblique incidence polarization interferometry method. With this polarization interferometer, not only can the flying height be measured down to contact without losing accuracy, but also the pitch and roll of the head-slider can be detected dynamically. The optical parameters of the head-slider can also be determined. Design details and experimental results are given.