Using the first-principles method based on density functional theory, we investigate the structural properties of seven different phases of BiFeO3 including R3c, R3m, P4mm, Cm, Pm3 m, R3 m and R3 c and structural transition. The results show that the ground state has the R3c phase, and that phase transitions can occur among these phases, which may be characterized by two types of structural transitions. One is the relative displacement between octahedral FeO6 and Bi3+, and the other is the rotation of octahedral FeO6 along the 111 axis. Furthermore, the BiFeO3 film is found to be able to change from R3c phase to P4mm phase, owing to the substrate effect.