The invention relates to a method for preventing over voltage of an inversion-side reverse polar wire of a high voltage direct current power transmission system, which adopts a special control method to make the trigger pulse of an inversion-side control system matched with the time sequence of an alternating current incoming line switch of an inversion-side converter transformer so as to achieve the effect of preventing the over voltage of the inversion-side reverse polar wire. More specifically, when an inversion-side converter valve of the direct current power transmission system is switched to a bypass for lockout and the reverse voltage of a direct current polar wire exceeds a set value, the control system sends out a command of switching to the bypass for lockout so as to prevent the reverse voltage of the direct current polar wire from further rising.