Abstract: It is very difficult to detect the crack of torsion bar of armored vehicles suspension system by ordinary nondestructive testing method. In order to detect the crack damage of torsion bar expediently, the method for crack detecting by AE technique under loading condition was given. Based on the principle of virtual instrument, a detecting hardware system was built, using the devices, such as portable industrial control computer, data acquisition card, high sensitive sensors and manual hydraulic loading device. Also, appropriate detecting and locating software system were programmed. The studying process and the nondestructive detecting system built for this study were summarized and analyzed. The crack of torsion bar tested was detected successfully in the experiment on real equipment. And the following result can be found out: the dynamic detecting method based on AE technique is an effectual method to solve the problem that is difficult to detect crack damage of torsion bar under static condition.