Through combining the ranging equation and optimization, a new method of fault location based on ant colony algorithm is presented to resolve the difficult ranging equation. Based on the distributing parameter transmission line model, the common positive sequence fundamental frequency fault component is obtained after decoupling the line parameters, the fault location function is educed according to the principle that the amplitude of fault point’s voltage calculated from the two ends of a line is equal, then one unknown number and single peak function is constructed, and the ant colony algorithm is introduced to resolve the function. PSCAD/EMTDC proved it is reliable and accurate, the results of simulation indicate the algorithm is immune to the effect of fault type, power phase shift, fault impedance, fault position and other factors on locating precision, which has very strong practical value.