The effect of triple ion beams has been investigated by simultaneous and sequential irradiations of gold, hydrogen and helium on radiation damage in the CLAM steel developed in China. The depth profile measurements of positron annihilation Doppler broadening S parameter were carried out as a function of slow-positron beam energy to examine the produced radiation damage. The experimental results show clearly the synergistic effect of displacement damage and hydrogen and helium on the formation of radiation damage. The synergistic effect of simultaneous triple ion beam irradiation of gold, hydrogen and helium ions was found to suppress the radiation damage in the CLAM steel due to the helium and/or hydrogen filling of vacancy clusters.