Abstract: The ultrasonic computed tomography (USCT) method could record the arriving times of ultrasonic wave between the probes and the sources to calculate the elastic wave velocity in the section using the arrival times. Through analyzing the distribution of seismic velocity in aimed area, the information of the strength and the homogeneity of the investigated zone could be got indirectly. The operational principle of USCT was introduced. According to the calculation result of forward model in partially recording geometry and completely recording geometry and the difference of the inversion algorithm, the better algorithm was chosen and was used to detect the interior defects in large scale concrete structural member. Compared with other exploration methods, this method was more efficient and accurate.