We have calculated electronic structures of Fe0.5TM0.5Pt alloys (TM = Mn, Fe, Co, Ni, and Cu) using first principles calculations, which is based on the density functional theory (DFT). The calculated magnetic moments are -0.93 µB/u.c for Fe0.5Mn0.5Pt, 6.72 for Fe0.5Fe0.5Pt, 5.48 for Fe0.5Co0.5Pt, 4.74 for Fe0.5Ni0.5Pt, and 4.01 for Fe0.5Cu0.5Pt. It is noted that Mn is anti-ferromagnetically coupled with Fe, while Fe, Co, Ni, and Cu are ferro-magnetically coupled with Fe. This is attributed to that the exchange integral (Jex) between the Fe and TM changes from the positive (Fe, Co, Ni, Cu) to negative (Mn). The magnetic moment and Jex are dependent on the number of d-band electrons/u.c., i.e. neff. It was found that the magnetic moment of Fe increases from 2.28 for Fe-Mn-Pt to 3.06 µB for Fe-Cu-Pt, but the magnetic moment of TM element increases or decreases after alloying.