The synergistic effect of triple ion beams is investigated by simultaneous and sequential irradiations of gold,hydrogen and helium ions on the low activation martensitic steel (CLAM) developed in China.The depth profile measurements of the positron annihilation Doppler broadening S parameter are carried out as a function of slowpositron beam energy to examine the produced radiation damage.The synergistic effect of displacement damage and hydrogen and helium on the formation of radiation damage is clearly observed.In the preset case,this effect suppresses the radiation damage in the CLAM steel due to the helium and/or hydrogen filling of vacancy clusters.