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The frequency domain of ultrasonic pulse echo signal obtained from carbon fiber reinforced polymer (CFRP) was studied. First the frequency domain feature of reflection coefficient for the fiber layer and resin layer in CFRP laminate was analyzed. The result shows that normal and porous fiber layer, and normal and thick had different influence on the acoustic reflection coefficient. Based on the result above, the frequency domain model for the pulse echo signal acquired from CFRP laminate was established. The pulse echo signal spectrum was composed of normal fiber/resin layer response, porous fiber layer response, thick resin layer response, probe response and noise signal response. Then the numerical simulation of CFRP laminate was implemented based on the model. The simulation signal spectrum of CFRP laminate with voids as well as the spectrum of CFRP laminate without voids was obtained. The results show that the simulation signal spectrums had the same main frequency components with the corresponding experimental signal spectrums.