In recent years, impedance measurement method by piezoelectric (PZT) wafer active sensor (PWAS) has been widely adopted for non-destructive evaluation (NDE). In this method, the electrical impedance of a bonded PWAS is used to detect a structural defect. The electro-mechanical coupling of PZT materials constructs the original principle of this method. Accordingly, the electrical impedance of PWAS can sense any change in the mechanical impedance of the structure. A thermal stress on a structure, which was generated by environmental temperature, could change the electrical impedance of PWAS. The thermal stress which affects the output impedance of PWAS is also developed. A temperature-dependent model, the temperature dependency of PWAS, and structure material properties are investigated for a PWAS bonded to an Euler Bernoulli clamped-clamped beam. The Rayleigh-Ritz and spectral element methods are studied and, then, verified by 3D finite element method (FEM).