Abstract: Principle of deck thickness radar detecting was introduced. Non-destructive test of three bridges in the Beijing-Zhuhai expressway was carried out by use of Handy scan ground penetrating radar produced by GSSI company of the United States. Radar signal processing software Radan was used for digital signal processing to the detected radar image, including suppression of random and regular interference, filtering frequency, improving the resolution. The processed continuous and clear image showed that the deck thickness changed along the test line. Useful parameters in the reflected wave were extracted for the layers thickness calculation of multi-point of each span. Average thickness of three layers of each span was calculated. The application research showed that the ground penetrating radar with center frequency of 1 GHz could detect the depth about 20cm in concrete structures, which was shallow detecting ground penetrating radar. It can detect three layers of the bridge deck. The test result was not obvious for the fourth layer because of its long distance from the surface. Radars with lower center frequency are recommended to detect the fourth layer of the bridge deck. The test result of thickness of bridge deck by the ground penetrating radar is reliable and can be the basis for evaluation of the project quality.