Abstract: A magnon-phonon interaction model is developed in two-dimensional insulating ferromagnet of which the magnon spectrum is studied in accordance to Matsubara-Green function. The magnon dispersion curve is calculated on the main symmetric points lines in Brillouin zone for different parameters in the system. It is found that at the boundary of the zone the magnon linewidth broadens and magnon softens both most obviously. The influences of longitudinal phonon and transverse phonon on magnon softening and magnon linewidth broadening are compared, and the influences of different parameters on them are also illustrated.