Abstract: In this paper, with the comparison and analysis of the data of Ship-borne X-band wave measuring radar in two offshore operations, it is found that the high value of significant wave measured by the radar has a large error in a period of time. During the period from 10:00 to 17:00 on December 6, 2017, the value of significant wave height measured by the radar continued to be lower compared to the visual observational value. By analysing the weather and environmental conditions on the site and comparing the two-dimensional wave spectrum at different times under the same sea condition whether it was affected by the rainfall, we know that the rainfall and poor visibility occurred during this period had resulted in abnormally low wave spectrum energy on the radar. This would lead to a low SNR of radar inversion, further resulting in the small significant wave height measured by X-band radar. The radar measured significant wave height consistently higher than the buoy values when the vessel passed by the no. 5 and no. 4 buoys on April 11, 2018. Looked at the maximum flow rate setting in the system, it is found that the maximum flow rate set is over 50m/s. As a result, the bandwidth of the filter is too large and a great amount of noise as wave signals, might have passed through the filter resulting in a higher SNR of radar inversion and a higher value of significant wave height measured by X-band radar. It is valuable for both adjustment of radar setting and the further improvement of radar system by the error analysis.