Fiber metal laminates are widely used in large aircrafts. Debonding occurs easily at the bonding interface due to process and environmental factors, affecting its performance. It is essential to effectively detect and evaluate the bonding layer. This study proposes a method for evaluating the micro-debonding degree of adhesive interfaces using local defect resonance (LDR). Under the nonlinear mechanism of contact acoustics, the defect is regarded as a nonlinear spring oscillator, and its LDR frequency is determined. Numerical simulation is used to analyze the resonance under different excitation conditions. The experimental object is a glass fiber aluminum alloy bonding plate with different sizes of debonding defects. Piezoelectric actuator/sensor units are pasted on the surface, excitation signals with different frequencies are applied to the actuator according to the LDR frequency, and the spectral analysis of the response signals is conducted. The simulated and experimental results show that the nonlinear feature of the debonding interface can be improved based on the LDR effect. In addition, LDR frequency can be employed to determine the debonding damaged area.