Abstract: Doppler radar data quality are seriously affected by trans-horizon ground and sea echoes in ducting conditions. Aimed at influence of the atmospheric duct on sea echoes, based on the weather radar and the sounding data from Qingdao station, one case of the atmospheric duct that took place on July 18−19 is analyzed. The sounding data indicates that a surface duct exists at 20: 00 July 18, and the radar data indicates that the trans-horizon sea echoes exist simultaneously. During this atmospheric duct process which lasted for about 24 hours, trans-horizon sea echoes received by the weather radar showed a general tendency of weak to strong, and to weak, and disappear in the end. The radar echoes have complex distribution and variation within this case. Range-depended ducting profiles are estimated from the radar echoes, the results of small difference show the effectively of the methods of calculating radar echoes and retrieving ducting profiles.