Glide-slope is an important part of the instrument landing system (ILS) offering vertical azimuth guidance for approaching aircraft. Accurate analysis of the influence of obstacles on the glide-slope signal can provide theoretical basis for the siting of a navigation facility and for the resolution of problems existing in the actual operation of the navigation facility. Based on the physical optics-physical theory of diffraction (PO-PTD) algorithm, combined with the Airbus A320-200 and the three-dimensional airport model, a static analysis of the influence is studied on glide slope approach. Based on the static analysis, a dynamic research is carried out on the influence from sliding aircraft on the taxiway meanwhile aircraft approaching in the final stage of airfield traffic pattern, which identified the cause of instability of the glide-slope signal reported by pilots for long time at an airport. Data of dynamic research is compared with the flight inspection result and found to be consistent with the flight inspection result.