The ultrasonic pulse signal resonance features in layered carbon fiber reinforced plastic (CFRP) within voids were researched.The frequency domain model of acoustic wave propagation in multilayered medium was established.Then the reflection coefficient of multilayered CFRP within voids was numerically calculated.The results are as follows.When the CFRP laminate is tested by ultrasonic whose center frequency is close to the CFRP inherent resonant frequency,the ultrasonic may generate resonance phenomenon in CFRP.If CFRP contains evenly distributed voids,the frequency of resonant signal and its amplitude all decrease with the increase of porosity.For the thick section CFRP within local concentrated voids,the local concentrated voids near testing surface will cause signal frequency reduction and the decrease of its amplitude.But the voids which exist in layers far away from testing surface almost have no influence on signal resonance.The ultrasonic pulse echo testing was conducted for thick section CFRP specimen.The analysis results of testing signals were in accordance with the results of the numerical calculation,showing that the reflection coefficient frequency response model can effectively explain the ultrasonic resonance phenomenon in layered CFRP within voids.