A multicast packet transmitting method of wireless network is provided. According to the method, a first transmitting terminal adds a first acknowledge serial number into a multicast downlink packet and transmits the downlink packet to a second transmitting terminal. After transmitting the downlink packet, the first transmitting terminal determines whether to re-transmit the downlink packet in accordance to a received second acknowledge serial number in an uplink packet, which is output from the second transmitting terminal.