Site preference behaviors of transition metal (TM) Cr and Ni in Fe3Al alloy and alloying effect are studied by using first-principles. Computational results show that the addition of TM is beneficial to the improvement of the stability of Fe3Al alloy; Cr atoms prefer to stay at FeI sites, while Ni atoms occupy FeII sites. Our investigations reveal that Fe2NiAl has lower bulk modulus B, shear modulus G and B/G than other (Fe3-yXy)Al (X=Cr, Ni; y=0,1,2) alloys, which turns out to be a brittle alloy. The analyses of density of states and electronic charge density indicate that additional TM improves the interaction between TM and neighboring host atoms of Fe3Al but weakens the interaction between Al and Fe.