Abstract: Based on the sounding data four times a day observed on related sounding station, R/V "Kexue 1" and R/V "Shiyan 3" during the South China Sea Monsoon Experiment (SCSME), the characteristic parameters of strong atmospheric ducts such as occurrences, duct height etc are analyzed using the cutoff wavelength formula. The results show that the probability of the lower strong atmospheric ducts occurring over the South China Sea (SCS) is about 30% during the Monsoon period and rises gradually from the north to the south of the SCS.However, the atmospheric duct heights are gradually low from north to south and 70% of occurred duct heights are within 1km height from the mean sea level.The total tendency of the daily variability of the probability of the occurrence and duct height is similar and shows "low-high-low" shape.The probability of the occurrence in the nighttime is a little bit higher than other time and duct height is lower and more stable in the late at night.