A communication system with train bus architecture is described. The communication system with the train bus architecture comprises a coupling device for transmitting a first instruction packet string having instruction packets via first path; the controlled module for receiving the first instruction packet string via first path, wherein the controlled module selects one instruction packet from the instruction packets, replaces the selected instruction packet by first response packet for forming second instruction packet string, and processes the selected instruction packet to generate a second response packet; and a terminal device for receiving the second instruction packet string via the first path, and for transmitting the second instruction packet string back to the coupling device via the at least one controlled module along a second path from the terminal device to the coupling device wherein the first path is connected to the second path to form train bus architecture.