The invention provides a communication device applied to an underground parking lot for communicating with a remote server. The communication device is provided with a communication module and a transmitting module, the transmitting module comprises an antenna unit and a gain unit, and the antenna unit is connected with the communication module; the antenna unit is configured to transmit a communication signal and receive a response signal sent by the remote server, the communication module is configured to generate a communication signal and process the response signal; and the gain unit is detachably connected to the antenna unit and is configured to amplify the signal strength of the communication signal and the response signal. In the underground parking lot, the situation that the communication signal strength is weak or even the connection is interrupted often occurs. The communication device provided by the invention adds the gain unit to the antenna unit, so that when the signal strength is weak, the gain unit can be connected to the antenna unit to enhance the signal strength of the antenna unit.