A communication terminal device is applicable to an aerial vehicle. The communication terminal device includes an antenna, an altimeter and a processing circuit. The antenna is configured to provide a transceiving range of electromagnetic waves. The flight height detector is configured to obtain an altitude measurement value adapted to specify an altitude of the aerial vehicle. The processing circuit is coupled to the altimeter and is configured to: determine whether the altitude measurement value exceeds a height threshold value; set the transceiving range of electromagnetic waves of the antenna to be omni-directional in response to determining that the altitude measurement value does not exceed the height threshold value; in response to determining that the altitude exceeds the height threshold value, execute an antenna beam width adjusting mechanism, so that the transceiving range of electromagnetic waves of the antenna is shaped into a directional beam.