For the detection of the weathering of stone relics, both gel-coupled and contact ultrasonic testing (without couplant) techniques are prevalently employed. However, these techniques harbor inherent challenges, such as potential contamination from couplants and the risk of relic damage during ultrasonic testing contact. The advent of air-coupled ultrasonic testing presents a safer alternative for weathering detection of stone relics, though its stability and applicability to weathering degree detection still require further validation. In this research, using sandstone samples from Yungang Grottoes, we conducted simulated weathering tests under freeze-thaw cycles and acid soaking conditions, where an air-coupled ultrasonic detection system was set up, and the ultrasonic velocity of sandstone samples was calculated based on the obtained original waveforms. Meanwhile, the samples of sandstone with different degrees of weathering were detected by gel-coupled and contact ultrasonic testing. The value of ultrasonic wave velocity and its variational trend with the weathering process were analyzed by means of the least squares regression model and oscillation coefficient calculation. As revealed by the results:1) the wave velocity dispersion of air-coupled ultrasound in repeated detection was significantly lower than that of the other two traditional ultrasonic detection techniques; 2) the obtained wave velocity was more consistent with the variational trend of weathering degree, featuring high applicability to the weathering degree detection of stone relics. In summary, presenting more accurate, safer and more effective weathering detection data, and having strong applicability and broad application prospects in the detection of stone relics, the air-coupled ultrasonic testing technique could provide important support for the conservation of stone relics.