A multi-channel transmission device is provided. The multi-channel transmission device includes a clock generator and a plurality of transmitters. The clock generator generates input clocks. The transmitters operate based on spread spectrum clocks respectively. Each of the transmitters comprises a phase rotator. The phase rotator provides a selection signal and an interpolation signal of multiple bits. The phase rotator selects two of the input clocks as a first selected input clock and a second selected input clock according to the selection signal, and generate a spread spectrum clock according to the interpolation signal, the first selected input clock and the second selected input clock.