As in the modal analysis of asymmetrical three-phase transmission lines， the Fortescue transformation matrix cannot attain the digitalization of the parameter matrices of the transmission lines， a simplified calculating method is proposed based on Fortescue matrix that can still play an important role in determining the exact modal transformation. By using the properties of the similar matrix of Fortescue matrix to simplify the calculation process， the corrected transformation matrix is applied in the mode component method. Error analysis of simulation results shows that the corrected transformation matrix is feasible in the fault analysis of asymmetrical transmission lines with smaller computational complexity and higher calculation accuracy.