Abstract: A new algorithm of restored pseudo heat flux(RPHF) based on heating-truncated data was proposed and its effect of heating period on the detectability of two kinds of defects, delamination and foreign insertions was tested. Periodic square waved thermography was conducted on the plates with heating periods of 10, 20, and 30 s respectively. The data collected from the inspections was processed by the proposed algorithm to obtain the restored pseudo heat flux. The signal to noise ratio of the RPHFs from the experiments with different heating periods were contrasted. The results show that longer heating periods, with the same total heating length, increase infrared detectability for the defects of high buried depths.