Owing to the shortage of transmission space, double-circuit HVDC on the same tower has been widely applied in the power construction. However, the electromagnetic coupling of different pole in two circuits makes the transient electrical characteristics complex when a fault occurs. The protection based on travelling-wave plays a main role in direct circuit protection, which makes great significance in the study of travelling-wave characteristics in double-circuit HVDC, so as to win the master of operating performance of line protection. As a result, based on the Bergeron line model, the method of phase-mode transformation and modulus calculation for line voltage and current when a fault happens in double-circuit HVDC is proposed firstly. Then the travelling wave characteristics in double-circuit HVDC and the difference from travelling-wave HVDC in single-circuit are analyzed systematically. After that, the influence factors of asymmetric transposition of transmission lines and frequency dependent parameter are taken into consideration. Finally, the theory is analyzed and verified in the platform of PSCAD/EMTDC. The results of this paper help to analyze the performance and the adaptability in double-circuit of the travelling wave protection based on single-pole electrical information.