The electronic,linear and nonlinear optical properties,structure and its stability of BiFeO3 during polarization reversal from reference cubic phase to ferroelectric R3c phase were investigated by LSDA + U method.In order to check if the transition path exits in experiments,we chosen to calculate the nonlinear optical second order coefficient which exist only in noncentrosymmetric structure.The relationship between the nonlinear optical second order coefficient and the Bader charge was also compared and we found the coefficient is also dependent on the Bader charge.We found that the charge transfer from Fe to Bi is a factor for the large second-order nonlinear optical coefficients,and O is the bridges of the process of charge transfer.In addition,the linear optical absorption coefficient was calculated; the obvious change in absorption peaks was observed during the transition.By comparing the crystal orbital of the reference cubic phase and distorted R3c phase we found that the hybridized Bi 6s and O 2p is the main reason that causes the structure distortion.