The invention discloses a method and device for detecting a line flashover fault. The method for detecting the line flashover fault comprises the steps that noise signals on a line around a tower are collected, the noise feature of the noise signals in the unit time is extracted, and whether the flashover fault of a power transmission line happens or not is detected according to the noise feature. According to the method and device for detecting the line flashover fault, windage yaw flashover and insulator arc-over can be detected at the same time, and the number of working devices is a half of the number of working devices used in a normal measuring mode; due to the fact that the structure of a detection system based on the noise signals is simple, the operation cost of equipment and the maintenance cost of the equipment are low, and working efficiency of maintenance workers can be greatly improved.