A method allocates physical addresses HDMI-CEC devices within an HDMI-CEC device network. The HDMI-CEC device network includes a plurality of HDMI-CEC devices consisting of at least two root devices, a plurality of parent devices, and a plurality of slave devices. Each of the root devices has a root ID. When a slave device is plug into an HDMI interface of a parent device, the parent device allocates a root ID and a physical address for the slave device. The slave device creates a route table according to the allocated root ID and physical address, to establish a serial communication with the parent device.