Abstract: The echo signal is inevitably affected by noise when coded ultra-wideband radar signal penetrates underground media, which makes data interpretation difficult. The f-k filtering method can effectively filter out part of the noise, but its filtering effect on the high-frequency bands is not good. To deal with this problem, an improved f-k filtering method is proposed in this paper, which sets different apparent velocity thresholds for sub-band processing according to the distribution of frequency and wavenumber. The apparent velocity threshold of high-frequency bands is increased, effectively filtering out the noise in the high-frequency band. The experimental results show that the entropy of the images processed by this method is reduced by 6% compared to that of the original method, which has a good noise suppression effect.