This paper presents a comparison of Gas-Insulated metal-enclosed transmission Line(GIL) and Gas-Insulated metal-enclosed Switchgear(GIS) bus and their applications with an example of Ling-ao Nuclear Power Station Phase II.The practice and experience accumulated on installation and adjustment of 500 kV GIL in tunnel for Ling-ao Nuclear Power Station Phase II is a good reference for the latter nuclear power station project.