The invention discloses a vehicle-mounted local discharge locating system for a mobile substation and a locating method of the vehicle-mounted local discharge locating system. Four radio frequency electromagnetic wave sensors are arranged on an automobile for receiving electromagnetic wave signals sent out from local discharge points, a signal conditioning circuit is used for amplifying and filtering the received signals, and a high-speed data sampling unit is used for synchronously collecting 4 paths of output signals and outputting the data to a data processing and analyzing unit so as to establish an equation set according to starting times when four radio frequency omnidirectional sensors receive ultrahigh frequency signals radiated by the same discharge source calculated in real time and on the basis of time differences of the four paths of received signals, solve direction angles and radial distances of the discharge signals and locate the discharge parts. According to the invention, all high-voltage equipment in the substation can be detected and located for local discharge, the cost for detecting the local discharge of the equipment can be greatly reduced, defects can be found out as soon as possible during patrol and inspection of the substation equipment, and accidents and interruption maintenance time can be reduced, so that the operation reliability and the intellectualization level of the substation can be improved and increased.