Abstract: Accurate and quantitative detection of internal defects in tunnel linings has always been a difficult engineering problem, and ultrasonic transverse wave imaging is the current cutting-edge technology for non-destructive testing of concrete defects at home and abroad. The response characteristics of ultrasonic transverse wave imaging at different frequencies are analyzed through model tests, and a quantitative identification method for internal defects in tunnel linings is proposed. In the ultrasonic imaging mapping, the color differentiation between the intersection of reinforcement, concrete and defects is obvious; when the ultrasonic emission frequency exceeds 25 kHz, the first layer of reinforcement can be effectively identified in the detection mapping; the ultrasonic emission frequency for better detection of conventional concrete internal defects is 45 kHz～55 kHz; the location of lining debonding defects can be identified according to the abnormal reflection area in the ultrasonic imaging, and according to the abnormal reflection Based on the depth of the abnormal reflection and the normal lining thickness, the thickness of the lining debonding defect can be calculated to achieve quantitative identification of internal lining defects. Through application in engineering and verification by borehole endoscopy, ultrasonic transverse wave imaging can effectively identify concrete lining debris defects quantitatively.