The effects of FeAl(B2) microalloyed with rare earth element (REEs) La, Ac, Sc and Y on structural, elastic and electronic properties are investigated by first-principles calculation based on the density function theory (DFT). The calculation results show that the REEs Y tend to be substituted for Fe site, while La, Ac and Sc tend to be substituted for Al site, and Ac causes the largest lattice distortion. The calculation results of elastic properties show that the ductility of FeAl(B2) is improved by the addition of La, Ac, Sc and Y. The Fe7Al8Sc has better ductility and hardness. The effect of REEs on the performance of alloy is attributed to the variation of hybridization between Fe and Al electrons. The calculation results are in accordance with experimental and theoretical results.