The Glide Slope (GS) uses the mirror principle to provide vertical guidance information for the aircraft in precision approach process,and terrain of the airport directly affects the vertical coverage performance of the GS.In this paper, the Antenna Distribution Unit (ADU), radiation field, Difference of Depth of Modulation (DDM) and angular displacement sensitivity of four types of GS are studied at first, and then comparison and analysis is made to the Beam Bend Potential (BBP) of different GSs.Finally, the influence of Forward Slope (FSL) on the vertical coverage performance of the GS is studied, and the corresponding compensation method is proposed.Combined with the terrain characteristics glide slope of the airport, it can provide a theoretical basis for the GS selection,installation and debugging.