The invention discloses an unmanned aerial vehicle distance measurement system and method based on distribution of an electromagnetic field of a power transmission line, and relates to the field of anunmanned aerial vehicle. Currently, when the unmanned aerial vehicle carries out distance measurement, a large measurement error exists. The unmanned aerial vehicle distance measurement system comprises a routing inspection unmanned aerial vehicle, an electromagnetic field sensor, a barometer, a data processing module and a flight control module; the electromagnetic field sensor, the barometer, the data processing module and the flight control module are all arranged on the routing inspection unmanned aerial vehicle; the data processing module is connected with the electromagnetic field sensor and the barometer; the flight control module is connected with the data processing module; the data processing module obtains a threshold of an electric field change rate at a height over the groundaccording to the electric field change rate and the magnetic field change rate which are obtained by detection of the electromagnetic field sensor on an electromagnetic field in terms of the height over the ground, judges whether the threshold is reached and transfers the threshold to the flight control module; the flight control module controls flight of the unmanned aerial vehicle and controlsflight of the unmanned aerial vehicle according to the tested thresholds of the electric field and magnetic field change rates; if the electric field change rate is smaller than the threshold, the unmanned aerial vehicle is designated to continuously fly according to an established flight; and if the electric field change rate is greater than or equal to the threshold, the unmanned aerial vehiclehovers and sends a too-close alarm signal to a control center.