Abstract: The broadcast authentication technology can protect broadcast information from pollution attacks for sensor coding network. Because the network resource is limited, and the broadcast authentication technology incurs new and lots of computational cost, the sensor coding network may suffer from denial of service attacks. In order to protect sensor network from pollution attacks and denial of service attacks, the broadcast authentication protocols are researched with the game theory. The probability of the pollution attacks is the crucial factor of the game. All Policies and actions of the middle nodes in broadcast authentication protocol are discussed, and the modes of broadcast authentication protocol are summarized. For the two game processes in the broadcast authentication protocol, forward first policy, authenticate first policy and combine first policy are researched deeply. Each policy’s cost and profit are quantified, and the two-phase game model of the broadcast authentication protocol is proposed. The Nash equilibrium of this two-phase game is the broadcast authentication protocol mode that each node should select. Each node uses the proper broadcast authentication mode according to the network environment, and network security and computational efficiency are improved simultaneously. The example shows the cost and profit quantification of policies are effective, and the game model is reasonable.