The invention provides an obstacle automatic detection alarm device for a power transmission line. A first clamping movement part is provided with a first support beam; the first support beam is provided with first traveling wheels; a second clamping movement part is provided with a second support beam; the second support beam is provided with second traveling wheels; a distance measurement instrument is clamped on the power transmission line respectively by the first clamping movement part and the second clamping movement part; the distance measurement instrument is provided with a travelingdriving mechanism, a driving motor control module, a controller, a distance measurement module, a wireless communication module and a storage battery for supplying power to electrical components inside the distance measurement instrument; and the controller acquires distance information between the power transmission line and an object around by the distance measurement module, and sends out an alarm to a monitoring end when the distance information is smaller than a preset threshold. The obstacle automatic detection alarm device provided by the invention is an intelligent alarm device capableof accurately measuring a distance. The obstacle automatic detection alarm device is flexible to move and reliable in distance measurement, actively gives an alarm, and transmits an alarm signal to amonitoring room to timely notify monitoring personnel to take an action.