A tray device includes a host module, a tray module, and a communication module communicated between the host module and the tray module. The host module includes a host recognition circuit, a host connection circuit, and a host controller electrically connected to the host recognition circuit and the host connection circuit. The tray module includes a tray recognition circuit, a tray connection circuit, and a tray controller electrically connected to the tray recognition circuit and the tray connection circuit. The tray controller determines an installation ordinal number corresponding to the tray module according to a recognition signal generated by the tray recognition circuit. The tray controller sends the installation ordinal number to the host controller by the communication module when the tray connection circuit generates a connection signal.