As a nondestructive testing technology, GPR has been become one of the most important tools in quality inspection of tunnel lining at present. It is widely applied to tunnel disease detection, such as the holes, cracks, voids between tunnel lining and surrounding rock, and it is also used to determine the steel arch distribution and lining thickness of tunnel. Through the application of GPR in a highway tunnel lining detection, response characteristics of reinforced bar and steel arch frame are analyzed on radar maps under different frequencies of radar. Through identifying abnormal reflection in radar maps and interpreting its reason, the number and arrangement of reinforced bar and steel arch frame can be obtained. Comparing with the tunnel design, good results are obtained.