First-principles calculations based on density function theory within the generalized gradient approximation (GGA) have been carried out to investigate the effects of O doping on the structural, magnetic and electronic properties of BiF3. Based on the calculated cohesive energies, O impurities prefer substituting F atom at tetrahedral sites (0.25, 0.25, 0.25). And the geometry of BiF3 changes little due to similar radius of O and F atoms. By analyzing density of states (DOS) of Bi4OF11 (II), it has been found that Bi4OF11 (II) presents magnetic character and half-metallic state, implying its potential applications in Li-ion batteries. Finally, the character of bond in Bi4OF11 (II) was discussed by analysis of charge density and bader charge. The result shows that O doping weakens ionic bond in BiF3.