An opportunistic network coding based broadcast transmission algorithm (ONCBT) is proposed to improve the transmission efficiency for wireless networks.ONCBT selects lost packets in a sorted order to generate the retransmission packet by XOR operations at sender
and retrieves lost packets from one or more retransmission packets at receivers.ONCBT has a priority to retrieve the lost packets owning higher time important level in each receiver with one retransmission packet
thus improving the transmission efficiency and packet transfer delay.The simulation results show that ONCBT can lead to higher transmission efficiency and lower packet transfer delay compared with other algorithms under typical wireless channel conditions.