Abstract: As X80 pipelines are applied in large scale, the safety of long-term service of long-distance oil and gas pipelines has attracted much attention. In order to solve the problem of detecting the inner surface crack defects of pipelines, experimental research has been conducted for the laser ultrasonic nondestructive detection method characterized by noncontact and high precision, which was also applied to the inner surface crack defect detection of X80 pipelines. The laser ultrasonic signals in the areas of X80 pipeline specimen with/without cracks and the laser ultrasonic based B-scan detection and imaging were obtained through experimental measurement. Meanwhile, the influence of crack defects on laser ultrasonic signal were analyzed. The research results indicate that: the inner surface crack defects of pipelines can be detected and accurately located through the laser ultrasonic based B-scan. Hence, the laser ultrasonic based B-scan is valuable for promotion and application in the nondestructive detection of pipelines.(9 Figures, 21 References)