Abstract: Since the majority structure of transmission line is the ring network, a new method for fault location in triangle network is proposed in this paper. This method is based on cubic interpolating polynomial and extraction of transient variable from fault disturbance. The fault line is identified by using the amplitude of voltage disturbance and current disturbance. The location of fault point in triangle network is calculated by the ratio of voltage disturbance on the line. The accuracy of this method is tested and proved by the simulating model with two generators and an infinite system. The results of simulating test show that the location of fault point is calculated very quickly and the needed number of measuring units is so little that huge investment could be reduced.