The influence of the phonon dispersion on the weak coupling polaron in monolayer graphene is investigated by using the linear combination operator and LLP unitary transformation method and taking account of the longitudinal optical (LO) phonons dispersion. The ground state energy and the zero-Landau level splitting energy in monolayer graphene as a function of the coefficient of the phonon dispersion are obtained in a parabolic dispersion approximation. Numerical calculation results show that the ground state energy increases with the increasing of Debye cut-off wave number, and the zero-Landau level splitting energy decreases with the increasing of phonon dispersion coefficient.