J55 steel pipe is a sort of oil extraction equipment which is commonly used for oil-pumping operation on some oil fields. Nonetheless, it is acknowledged that this kind of material is easily corroded in soil to some degree, which seriously restricts the life span of pipes. There is a feasible solution to this problem—to prepare a layer of corrosion-resistant coating onto the inner surface of the steel pipe. By means of Self-propagating High-temperature Synthesis (SHS) technology, a ceramic layer can be attached onto the inner surface of the steel pipe, which then requires nondestructive testing (NDT) in the process of product quality evaluation. Ultrasonic nondestructive testing (UT) technology is one of the effective means that can be employed in the inspection of this pipe. The processing of ultrasonic signals is the key problem of the detection. Concerning UT of ceramic-lined composite steel pipes, a novel flaw locating method based on fractal dimension is proposed. Ultrasonic A–scan method was implemented on different positions of a ceramic-lined composite steel pipe test piece. The fractal dimension of each curve of ultrasonic vibration time-domain signal was calculated. The transformation of each fractal dimension was compared and abnormal positions where defects potentially existed were found out. The result indicated that ultrasonic A-scan signal had an excellent fractal conduct characteristic. The experiment result also showed that it was feasible to compare fractal dimension of signal with the normal range and find out abnormal positions, which could provide basis for the following inspections.