With the appearance of radio frequency interference (RFI) in subsurface penetrating radar(SPR), this paper first analyzes the sources and properties of the RFI signal; and then based on the random property of RFI and the principle of mean square error (MSE),the wave-average filtering method in A-Scan and the median filtering method in B-Scan are discussed for RFI suppression. The performance of the two methods is demonstrated on data collected with SPR and the experimental results are also good.