The method of measuring absolute distance with the optical frequency comb of a femtosecond laser was proposed. A femtosecond laser was used as the light source of performing absolute distance measurement. A Michelson type interferometer structure was built. Exploiting the principle of the dispersive interference, the spectrum was analyzed. Then, the phase difference which was caused by the optical path difference of optical interference was obtained. Finally, the optical path length difference was measured. The experiment result shows that our length measurement method has high accuracy with the resolution of nanometer level. The minimum measurable distance is 9 μm, and the non-ambiguity range of length measurement is 5.75 mm. Compared to the limited measuring range of traditional white light interferometry, the maximum distance can be extended to arbitrary length.