The invention relates to a fault detection system and method for a power transmission line. The fault detection system comprises a main control circuit, a conductor vibration monitor, meteorological environment observation equipment, line monitoring equipment, a power failure detection module, a fault display module, a power supply module, a radio-frequency module, a fault detection module and a monitoring computer, wherein the fault detection module comprises a current sensor, a voltage sensor, an overcurrent protection module, an overvoltage protection module, a short-circuit fault judgment module and a grounding fault judgment module. In the fault detection device adopted by the invention, when a short-circuit fault occurs, an electronic switch can be automatically turned off within short time after being turned on; if the short-circuit fault is a transient fault, a current detection device detects no pulse current; if the fault is a permanent fault, the current detection device detects the pulse current, thereby whether the fault is the transient fault or the permanent fault can be judged, a reliable basis is provided for the subsequent fault handling and thus the inspection and maintenance speed of the line can be improved.