By calculating the switching overvoltage on the 500kV Fu-Ai compact transmission line

the results are obtained that the maximum phase-earth switching overvoltag along the line is 1.68p.u.and the maximum phase-phase switching overvoltag along the line is 2.85p.u.The air gaps 50% switching discharge voltages of representative working positions have been acquired by tested in imitative tower window

and the relationship between the approach distance of live line working and 50% switching discharge voltages are proposed.The risk rate under minimum approach distance of live line working on the straight line towers are obtained by caculation.The theoretical calculation and the test results prove that the risk rates is less than 1.0×10-5.The minimum phase-earth & phase-phase approach distance and the minimum comples gap safety distance are safe for live line working on the straight line towers of 500 kV Fu-Ai compact transmission line.