A land depression in urban problem is occured in the world. It causes a huge economic and human damage. it is mostly caused by a leakage of sewer pipe. Today, sewer pipe inspections are conducted in visual inspection by human or robots. In that case, visual inspection can not detect cracks in water. To detect cracks completely, a visual inspection should be replaced by other nondestructive inspections. In this study, we tried to find defects in a sewer HDPE pipe by using ultrasound inspection. we made a artificial defect pipe specimen and fabricated scanner system which use a pulse-echo method. We checked each crack ultrasonic signal of cracks. As a result, There are differences in each crack signal because of sewer HDPE pipe shape so each crack signals could be distinguished by each wave characteristics.