Abstract: The performance of HF surface wave radar(HFSWR) is limited by ionospheric clutter. In order to get characteristics and causes of ionospheric clutter, a method based on ionospheric sound is proposed. Based on traditional method which uses radar echo, ionosoude is introduced into HFSWR and the theory of wave propagation is application to analyze clutter. Characteristics and causes of ionospheric F layer clutter, Es layer strong clutter and a kind of "smile" type clutter are given by the analysis. Simulation and experimental show its effectiveness, and it can be useful in ionospheric clutter suppression.