Abstract: The quasi zero optical path difference (OPD) that Mach-Zehnder interferometer must meet is introduced. The scheme that the rough adjustment to the interferometer is performed with laser first, and then the fine adjustment to it is carried out with white light is provided for realizing the precision adjustment for OPD, according to the characteristics that the white light has high accuracy for adjusting OPD but is not easy to be cohered. The alignment principle, accuracy and indeterminacy of OPD for the coarse adjustment of Mach-Zehnder interferometer with laser is analyzed in detail. An improved laser coarse adjustment scheme is put forward to overcome the indeterminacy of OPD, which raises the order of magnitude of OPD accuracy from millimeter to micron, dwindles the dead zone of the white light fine adjustment greatly, and made the white light fine adjustment simple and feasible. The adjustment accuracy of final OPD for the interferometer is 1.6m.