Abstract: In order to measure the thickness of concrete structures, ground penetrating radar technology was used. The detection theory of ground penetrating radar was introduced. The system applied transmission antennas to launch high-frequency pulse electromagnetic wave(1 MHz~2 GHz) to the concrete structure, and while spreading along the path, its strength and waveforms would be adopted as the medium of electromagnetic property(dielectric constant) and the geometry. The main machine of Radar would receive the reflected wave, and in accordance with its double-layer propagation time t and calculated speed v to calculate the thickness of the layer structure. Through the thickness measurement of samples, the testing results showed that with thickness <400 mm, the detection maximum error was 6.7%. The on-site concrete bridge testing found that, for 120mm concrete slab cast-in-place, the standard measuring error was 5.29 mm, while for reinforced protective layer thickness and reinforcement of the larger spacing, the standard measuring error was much higher, which illustrated the less uniformity of the latter two. Testing results proved that it was practicable to measuring the thickness of concrete structures by Radar.