The joining of line arrester in insulator string in 35kV transmission lines sections which are easily stroked by thunder was researched. The electromagnetic transient simulation calculation model of 35kV transmission lines under the action of lightning wave was built. The influence of the line arrester on the lightning withstand level of 35kV transmission lines was simulated and calculated by electromagnetic transient software ATP-EMTP. The results show that the joining of line arrester can obviously improve the lightning withstand level of 35kV transmission lines, and is especially effective when the lightning directly strikes the conductor. When the lightning strikes the tower top, it is the tower grounding resistance that greatly affects the lightning withstand level. The lightning withstand level of 35kV transmission lines under various joining plans of line arrester were simulated and calculated.