Since there are different coupling characteristics of each side of the demarcation point for double-circuit HVDC transmission lines partially on the same tower, the approach to calculate the inter-refractive coefficient of every mode is obtained based on the phase-mode transformation in this paper. Then, propagation characteristics of fault travelling wave and criterion characteristics of travelling wave protection of single-pole-to-ground faults occurring in different line segments are investigated, and its differences from those on single-circuit HVDC lines and double-circuit HVDC lines are compared. It is shown that the travelling waves in the line-1 mode of double-circuit lines and earth mode of single-circuit lines can refract to passageways of each other, which is the important influencing factor for the propagation characteristics of double-circuit HVDC transmission lines partially on the same tower combining the extreme features of single-circuit HVDC lines and double-circuit HVDC lines. In terms of traveling wave protection based on modulus component, the influence of the traveling wave characteristics mainly embodies in the line-mode wave change rate. The size of line-mode wave change rate is between single-circuit HVDC lines and double-circuit HVDC lines and is related to the total length of single-circuit lines in double-circuit lines partially on the same tower. This work is supported by National Natural Science Foundation of China (No. 51577072).