Abstract: In order to master the statistical characteristics of atmospheric duct in the South China Sea more accurately, the sensitivity of atmospheric refractive index of temperature, pressure and humidity are analyzed in detail. Based on the cruising GPS sounding data in the South China Sea from the year of 2006 to 2010, statistical analysis of the occurrence probability of surface-based duct and elevated duct, and their characteristic parameters are computed and analyzed. The results show that the average occurrence probability of surface-based duct is relatively low, generally less than 20%. The average height of the top of surface-based duct is about 167 m, and the thickness of the trapped layer is below 30 m. The strength is between 4.5 M-units and 9.6 M-units, and the annual average is 7.5 M-units. While the average occurrence probability of elevated duct is near to 50%, and the height of the top of elevated duct is generally between 1 100 m and 1 300 m. The thickness of the trapped layer is at an average value of 32.8 m, which is slightly higher than that of the surface-based duct. The average strength of elevated duct is close to that of the surface-based duct, but its span is much smaller. These results can provide reference for the operation of ship-borne radio system in the South China Sea.