The method of transmitting data in real time with low power via a wireless line in which channel status is searched to prevent data loss by transmitting and receiving retransmission a packet every time when there is an interference, and to minimize power consumption necessary for transmission and reception by transmitting and receiving the retransmission packet at a specific period when there is no interference. The method includes: transmitting real time packet data containing reply requesting information from a master to a slave; determining channel status by analyzing whether the master receives the reply packet and reply information; and adjusting the number of times of requesting the reply packet by selectively recording the reply requesting information contained in a control information field of the real time packet data according to the determined channel status. Power consumption due to the transmission and reception of the reply packet can then be reduced.