To meet the current demand for obstruction testing of airport clearance zone, the electronic theodolite, laser range finders and GPS capabilities are integrated, and an airport clearance intelligent monitoring instrument is developed. According to the electromagnetic wave's principleof measuring distance and the actual count rate, the precision of monitor's measuring distance is obtained.By specific analysis through error propagation of trigonometric leveling for obstacle in clearance zone and various errors, which includes side length error, observation error of the elevation angle, refractive error, such as error of the instrument height and sighting point height. etc., and in combination with the precision requirements of obstacle measurement by domestic and international civil aeronautics organization, the height precision requirements of monitor instrument is obtained through comprehensive analysis. Finally technical requirements for measuring distance accuracy ± 0.5 m and elevation accuracy ± 1 m are got by analysis and appraisal, which provide a theoretical basis for determining the main technical parameters of the airport clearance intelligent monitor and the selection of the appropriate instrument module from the market.