Induced current and power loss and impedance of busbar used in 550kV/4000A SF6 GIS under normal situation were calculated for different tube material thickness in multiple-point-earthing system and single-point-earthing system.The effects of earthing system and tube material and thickness to the loss power and impendence were compared in detail.In multiple-point-earthing system

if the tube material was aluminum or stainless steel

the power loss would decreasing as tube thickness increasing;but if the tube material was boiler steel

the power loss almost didn’t change when the increasing of tube thickness;the power loss of stainless steel and boiler steel would be 14 times and 32 times of that of aluminum respectively.In single-point-earthed system

the power loss increases with the increase of wall thick of tube.If the material of tube is aluminum or stainless steel

the power loss of tube in single-point-earthing system was much less than that in multiple-point-earthing system;if the material was boiler steel

the power loss in single-point-earthing system was 2 times of that in multiple-point-earthing system.These were determined by distribution character of induced current in the tube.