The reflection characteristics of the electromagnetic waves in the concrete linings of tunnels are studied. The identifying of the reflection characteristics of the lining voids, steel ribs, reinforcement bars, re-bar protection thickness, water seepage, lining thickness and lining internal defects in the quality inspection of tunnel linings by means of the waveform records and radar imags are expatiated on basis of engineering cases, so as to evaluate the quality of the tunnel linings.