Abstract: Structural stress, as a typical environmental factor, can significantly influence the propagation characteristics of ultrasonic guided waves. In this study, a dispersion analysis model for prestressed plate-shell structures was developed by combining the Murnaghan hyperelastic constitutive model with acoustoelastic theory, and its accuracy was validated through acoustoelastic guided wave experiments. The effects of arbitrarily applied multiaxial prestress on the dispersion curves, displacement field structures, and phase velocities of guided waves in polyethylene plate-shell structures were analyzed for different propagation angles. A stress sensitivity factor was introduced to quantify the sensitivity of various guided-wave modes to structural stress across different frequencies. The results reveal that an in-plane non-uniform stress state induces coupling between the displacement fields of Lamb and SH waves, thereby altering the trend and distribution of dispersion curves. Under multiaxial prestress, the phase velocity variation of guided wave modes can be approximately decomposed into a linear superposition of individual uniaxial stress effects. Moreover, the SH₀ mode and the Lamb-A₀ mode in the frequency range (>20 kHz∙mm) exhibit relatively low stress sensitivity, making them suitable excitation modes to effectively suppress signal interference caused by structural stress.