The invention realizes an ultra-high voltage transmission project line lead direct lightning current inversion method and system. By establishing a simulation model, the actual running condition of the ultra-high voltage transmission project line can be completely simulated, and after the wave impedance parameter, the running mode and the lightning strike position of the simulation model are fixed, the wave-head time and amplitude of the actual lightning current are obtained by the simulated lightning current in the simulation model according to the inversion method. Meanwhile, according to whether the trip-out condition occurs in the lightened actual line, different magnitudes of simulated lightning current is applied to the simulation model, so that the determination time is saved. The inversion method is easy to operate and realize and low in operand, and considering the running mode of the transformer substation of the ultra-high voltage transmission project line, the equipment parameter, the lightning strike position, and wave-head time and amplitude of the lightning current, the lightning current parameters of the actual line can be accurately determined and the subsequent work can be conveniently carried out.