Restart function is generally required to be withdrawn during live working on UHVDC transmission lines，but extra withdrawal may reduce the safety operation level of power system． Thus，safety analysis about live working on UHVDC transmission lines with restart function is necessary． Firstly，the effects of withdrawing restart function is analyzed． And then，in consideration of using restart function and according to the maximum switching overvoltage level of UHVDC transmission lines， the safety distance for live working is calculated． Finally，combined with the typical live working projects on DC transmission lines，the feasibility of live working with restart function is analyzed． The results show that tower head air gaps of UHVDC transmission lines can meet the requirement of minimum safety distance for live working． In all kinds of live working projects， restart function should be withdrawn once phase － ground or phase － phase insulated bearing tools are used，and otherwise it can be used．