A new infrared preprocessing modality called sequence differential processing is proposed. Different from the cold image subtraction which only decreases the background noise, the proposed modality takes the parallel test into account to preprocess the raw thermal data sequence prior to applying the advanced postprocessing techniques such as principal component thermography and pulsed phase thermography. The results show that the preprocessing method not only effectively reduces the influence of uneven laser energy distribution on detection efficiency but also enhances internal defect information. Moreover, the combination of the proposed preprocessing method with the pulsed phase thermography and principal component analysis algorithms improves the ability of laser infrared thermography to detect defects inside aviation carbon-fiber-reinforced plastics.