Inelastic neutron scattering spectra of LaNi4.5Mn0.5Hx (x=1.2, 4.2, 5.6) have been measured using berylium filter detector spectrometer. From the spectras, it was found that the second and the third peak of optical branches shifted 6 meV and 10 meV towarcs high frequency respectively, and the M-H bond in LaNi4.5Mn0.5Hx became stronger than that in LaNi5Hx, after the same part Ni of LaNi5 was replaced by Mn. Finally, we explained the cause of this phenomena in brief.