In this paper, propagation of harmonic plane waves is considered in a linear thermoelastic an infinite cylinder for an isotropic material has been investigated. The effects of a magnetic field in a propagation of harmonic plane waves is considered in a linear magneto-thermoelastic an infinite cylinder. A finite difference method is proposed to obtain the solution of the transient coupled thermoelasticity in an infinite cylinder with its base suddenly subject to a heat flux of a decayed exponential function of time. The present method is a second-order accurate in time and space and unconditionally stable. A numerical method is used to calculate the temperature, displacement components and the components of stresses with time t and through the radial of an infinite cylinder. Comparisons have been made with the obtained results in the presence and absence of the considered variables and displayed graphically. The results indicate that the applicable of the phenomena in diverse fields as biology, astronomy, petroleum extracting. The findings show that the impacts of the magnetic field is very pronounced.