The effect of ordering degree on the electronic structures and magnetism of Fe3Si alloys are investigated scientifically using first‐principles calculations based on plane‐wave pseudopotential theory. The studied results of the heat of formation and cohesive energy for D03 and B2 structures of Fe3Si reveal that the order of structural stability from high to low is B2‐9, B2‐8, B2‐7, B2‐6, D03/B2‐1, B2‐2, B2‐3, B2‐4, and B2‐5. Both D03 and B2 structures of Fe3Si exhibit the metallic feature. A wider breadth of the pseudogap with occupation of Si sites by more Fe[B] atoms except B2‐5 implies that the hybridization and covalent bond are intensified. Meanwhile, with substitution of Fe[B] atoms by more Si atoms, the stability of the system improves because the Fermi level is nearer to the bottom of the pseudogap. The origin of ferromagnetism for ordered Fe3Si except B2‐9 is mainly from the Fe 3d spin polarization. Compared with D03 structure of Fe3Si, an increment in the concentration of Fe atoms with occupation of Si sites by more Fe[B] atoms causes the change of interaction between Fe and Si atoms and the total magnetic moment increases. On the contrary, the total magnetic moment decreases with gradual substitution of Fe[B] atoms by Si atoms.