Embodiments of the present invention provide a line initialization method, a device, and a system. The method includes: when a new line is added, releasing at least one resource unit that is on a line at a Showtime stage, so that on the line at the Showtime stage data is transmitted on a remaining resource unit that is obtained after the at least one resource unit is released; performing basic initialization on the new line by using the at least one resource unit or a subset of the at least one resource unit, so that after the basic initialization, data can be transmitted on the new line by using the at least one resource unit or the subset of the at least one resource unit; and performing crosstalk cancellation initialization on the line at the Showtime stage and the new line by using all resource units.