MAC protocol of Wireless Sensor Network (WSN) requires high efficiency to achieve maximum traffic transmission, while pursuit high reliability at the same time. The paper researched on reliable mixing broadcast implementation manner of WSN. Based on analysis on implementation manners of broadcast, unicast and mixing broadcast, a kind of adaptive MAC protocol supporting reliable mixing broadcast was presented. The protocol dynamically select implementation manner with maximum mixing broadcast efficiency based on given network parameters to complete transmission of data frame. Simulation results based on NS2 shows that the protocol has better performance to achieve reliable mixing broadcast, which solve problems of reliable broadcast/multicast at network layer.