Abstract: The performance of the high frequency surface wave radar (HFSWR), which works at the shortwave band (3-15 MHz), degrades heavily in an intensive radio interference environment. The radio interferences must be suppressed to ensure HFSWR all-weather operations. Polarization filtering is an effective method to suppress radio interferences, but the polarization parameters of signal and interference must be accurately estimated. On the basis of polarization parameters exact estimation by fractional Fourier transform (FrFT), a subspace is constructed using those estimated parameters, and the oblique projection operator is used to suppress radio interferences for HFSWR. The processed real data indicate that: the polarized parameters of the target and the radio interference can be estimated exactly by FrFT; the radio interferences can be effectively suppressed; the detection performance of HFSWR is further improved.