The response of thermoacoustic waves propagating in a thin plate exerted by mechanical stress is characterized by the phase velocity dispersion curves and attenuation spectra in this paper. The stressed thin plate is assumed to be insonified by an intensity modulated CW laser which is modeled as a Gaussian beam. The constitutive relations and governing equations are formulated within the framework of acoustoelasticity and thermo-elasticity. Attenuation spectra in the vicinity of folding frequency can be used as a significant index correlative to residual stress in the specimen. The amplitude and phase of thermoacoustic response are sensitive to the mechanical stress applied to specimen if loading direction is parallel to the direction of wave propagation.