A scan lens and an interferometric measuring device using the scan lens are disclosed. The scan lens includes a lens set, a beam splitter, and a reflector disposed between the lens set and the beam splitter. During application the applied light beam passes through the lens set of the interferometric measuring device to fall upon the beam splitter where the light beam that passes through the beam splitter is defined as a first light beam and the light beam that is reflected by the beam splitter is defined as a second light beam. The first light beam is projected onto the test object. The second light beam is projected onto the reflector. The second light beam reflected by the reflector and the first light beam reflected or scattered by the test object will interfere with each other to form interference patterns for measuring the test object.