The invention discloses a direct current power distribution network interpolar fault rapid protection method. A fault transient electrical quantity and a line RL model are used to solve an inductanceparameter of a line, and a fault line is determined according to a size of the inductance parameter. In order to further improve sensitivity of this method, a small boundary inductor is connected in series to a head end of each line, and an inductance voltage is used to replace differential in the line RL model so as to eliminate a truncation error when a difference is used to replace the differential, reduce a calculated amount when a line inductance parameter is calculated, simultaneously simplify a calculation process, and reduce a requirement of an algorithm to a sampling rate.