Influence of the length and the diffusivities of the samples on measured results and the applicability of the photoacoustic piezoelectric (PAPE) technique have been studied according to a simplified thermoelastic theory of the PAPE method. The PAPE technique based on a simplified thermoelastic theory was proposed. The relationship between the amplitude and phase of the PAPE signal and the frequency modulation were confirmed. Simulations were performed to investigate the measurement accuracy of the different materials with the same thickness and the identical materials with different thicknesses. For proving theoretic results the experimental system was developed to research for thermal diffusivities of red copper, aluminum, brass, iron and steel (C: 0.5%) whose thicknesses of is 2 mm. In addition, the thermal diffusivities of aluminum and brass with different thicknesses were also investigated by the experimental system. It shows that the PAPE technique can be employed for the accuracy measurement of the samples of the better heat conductivity properties and the thicker length.