Mechanical delay line has been used in the Michelson interferometer to see the geometry and internal structure of objects. This method has to change the optical path length of a reference arm to match with that of a sample arm. However, its reference mirror must be continuously moved for depth scans, it requires a long time because it is limited by mechanical movement speed. We proposed and demonstrated an high speed optical delay line using two phase modulators in optical coherence tomography for axial scanning. Experimental setup is consist of pulse laser source (center wavelength 1304nm, pulse width 30ps, repetition rate 10GHz), two phase modulators and dispersive shifted fiber. As experimental results, the system has high scanning speed of 120km/s and a high repetition rate of 10MHz were achieved.