The ablation fault of buffer layers in high-voltage cables is a frequent type of cable fault in recent years. However,current detection methods for ablation defects cannot meet the detection requirements of existing cables. In this paper,the ultrasonic detection method for the buffer layer ablation defects in high-voltage cables based on the surface roughness of aluminum sheath is studied for the first time. Firstly,simulated buffer layer ablation experiments under humid conditions are carried out,and the laser confocal microscopy and electrochemical impedance spectroscopy analysis are carried out on the ablated aluminum specimens. It is found that with the increase of ablation time,the surface roughness of aluminum specimens gradually increases,and the surface corrosion degree of aluminum specimens gradually deepens,corresponding to the aggravated ablation defects of buffer layers,which indicates that the surface roughness of aluminum specimens could be correlated with the ablation degree of buffer layers under the moisture conditions. Secondly,ultrasonic testing experiments are carried out on the ablated aluminum specimens,and the roughness of the corroded surfaces of aluminum specimens can be calculated from the amplitude ratio of adjacent ultrasonic echo signals. The calculated results show the same variation trend as the measured roughness in the experiment. The results in this study indicate that the ultrasonic tests could be used to detect the severity of buffer layer ablation defects,providing the research basis for the ultrasonic detection method of ablation defects in the buffer layer of high-voltage cables.