Over the past two decades, significant advances have been made in the use of high frequency surface wave radar (HFSWR) for remote sensing in an ocean environment. As one of the main outside interference, ionospheric interference may badly affect radar's performance. An effective method for ionospheric interference suppression in HFSWR based on time-sharing coherent side-lobe cancellation (CSLC) is presented. Experimental results acquired with the HF system OSMAR confirm that the method can achieve effective ionospheric interference suppression, but not decreasing the strength of the first-order sea echo.