Explosion-proof sheets are key components in ensuring the safety of lithium batteries. These aluminum sheets easily cause welding perforations, broken welding, and false welding during the welding process using laser welding technology. Presently, inspection mainly relies on visual inspection and visible light image detection; however, these detection methods cannot detect faulty welding. Here, we propose a pulsed infrared thermography technology to detect laser welding defects. Four specimens with welding ratios of 100, 50, 33, and 25% were fabricated. The signal reconstruction method eliminates the influence of the uneven surface of the specimen. It is shown that the larger the welding percentage, the larger the bright spot in 1D images of the welding area. The binary segmentation of the 1-D image indicated that the laser welding percentage and detection area have a positive linear correlation, which verifies the effectiveness of the pulsed infrared thermal imaging technology for lithium battery explosion-proof sheet welding quality inspection, providing a new method for detecting the welding quality of lithium battery explosion-proof sheets.