In order to make full use of the efficiency of composite material tower,it is studied to cancel the overhead grounding wire and downward leading wire to form fully insulated tower. Considering loss of discharging path when insulated tower is stroked by lightning, overvoltage caused by resulting intruding wave may do damage to equipment in substation, iron tower is proposed to be used in inlet line to relieve the overvoltage. Lightning withstanding levels of insulated tower and inlet line iron tower are simulated by ATP-EMTP, and the impact of lightning intruding wave on inlet line iron tower and substation, and the necessity of arrester is also studied. The results show that when arresters are not installed, the lighting intruding wave overvoltage(LIWOV) caused by lightning current of 9 kA on 110 kV insulated tower could result in flashover of inlet iron towers and about 800 kV overvoltage on a typical 110 kV substation, while LIWOV withstanding level of iron tower is improved up to about 40~45 kA lightning current and consequential overvoltage of less than 300 kV stressing the substation after installing arresters, which fulfills the requirements of the standard.