An infrared thermal wave radar imaging system was set up to detect the internal CFRP laminate defects. Two novel kinds of signal extraction algorithms named Chirp lock-in algorithm and HT algorithm based on Hilbert transform and Fractional Fourier transform were developed in order to obtain the characteristic information of thermal wave radar signal. The defect size distribution range and criteria of defect judgment were designed reasonably. The influence of signal extraction algorithms on the probability of detection was studied by means of Hit/miss analysis methodology. The POD curves obtained by the proposed algorithms at the designed testing parameters and thresholds were given. According to the probability analysis of detection, the probability level of CFRP laminate defects detection using infrared thermal wave radar imaging system were identified.