Conventional protection of double － circuit transmission lines on the same tower trips and recloses the two circuits independently after the faults occurring in transmission line． The possibility of tripping all lines is high when inter － circuit faults occur． Large amount of load will be rejected and electrical link between two sides will be disconnected，which has negative effects on the stability of power system． A novel tripping and reclosing strategy is proposed which regards the double circuits as a whole． It can decrease the possibility of tripping all lines and reclose to permanent faults． The feasibility of quasi － three － phase operation ( QTPO) is analyzed． A typical model of double － circuit transmission lines on the same tower is established in PSCAD/EMTDC． Some important electrical indexes which can reflect the performance of QTPO are analyzed by simulation．