Abstract: The radiation induced segregation (RIS) was studied by electron/helium dual-beam irradiation. Within a grain, the content of Cr and Mn were higher in the center than at the margin of the irradiated areas. In the contrary, withim the irradiated areas included grain boundaries the contents of Cr and Mn decreased at the grain boundaries. RIS was weaker under dual-beam irradiation than that under electron single-beam irradiation, which was because of the increases of dislocation density and sink strength of voids when helium existed.