A method for transmitting data via multi-channel communications is provided. The method comprises following steps: providing transmission modes to be selected and determining transmission channels and transmission modules corresponding to the selected transmission modes; splitting a piece of data to be transmitted to a number of data segments, the number of the data segments being same to a number of the determined transmission channels; labeling a sequence number to each data segment; distributing the labeled data segments to determined transmission modules correspondingly; and transmitting the labeled data segments via the corresponding determined transmission channels. A system and a transmission device for transmitting data via multi-channel communications are also disclosed.