During the landing and gliding process of aircraft, enough vertical distance should be maintained from the overhead power transmission line approaching or passing through the end clearway of the flight area, so as to prevent disturbances on airborne navigation electronic equipments. According to various performance and protection levels of different aircraft landing systems, the radio interference level was analyzed and the interference protection ratio was checked. Combined with the characteristic of glide slope distance and related standards, the distance requirement and protection distance of the key points of glide slope was calculated. The result shows that for double-beacon landing system, the vertical distance of 150 m is required between the glide slope and power transmission line, and that for the prevalent meter landing system, the vertical distance should be calculated according to the emitting direction of glide beacon and flight procedure, the 150 m vertical distance is of redundant safety.