Abstract: A magnon-phonon interaction model is developed on the basis of two-dimensional triangular insulating ferromagnet. The magonon spectrum is studied through Matsubara-Green function, and the magnon dispersion curve is calculated on the main symmetric point and line in Brillouin zone for different parameters in the system. It is concluded that at the boundary of Brillouin zone magnon linewidth broadening and magnon softening are both enhanced. The influences of longitudinal and transverse phonon on magnon spectrum softening and linewidth broadening are compared and discussed, as well as the influences of other relevant parameters and temperature change. The following conclusions are thus drawn: (1) The closer the magnons come to the boundary of Brillouin zone, the more intense the magnon-phonon coupling and the clearer the magnon softening; (2) The vibration of magonon spectrum is irrelevant to the intense of magnon-phonon coupling; (3) The smaller the stiffness constant of spin and the lower the Debye temperature ΘD of the material, the clearer the magnon softening; (4) Below the transition temperature (Tc) of ferromagnetic, the higher the temperature, the clearer the magnon softening; (5) On the Σ line (including the point Γ, M) and Z line (including the point M , K) , the longitudinal phonon have greater influence on magnon softening than the transverse one.