  In this paper we calculate ab initially the phonon dispersion relationship of
the superconductor LaFeAsO and investigate a main property in the
superconductor, the oxygen isotope effect. Based on this phonon dispersion
relationship, we find the fact that an important reason of the oxygen isotope
effect is connected with the phonon. This result agrees well with the
experimental data where the power index of the oxygen isotope effect in the
superconductor LaFeAsO is small.
