Broadcast authentication is an important security primitive in wireless sensor networks. Costs of Tree- based muTESLA are rising rapidly with more senders in networks, which limit its use in large-scale networks. To removing such a limit, this paper presents a muTPCT-based broadcast authentication protocol which mainly rests on constructions of muTPC (muTESLA parameters hash chain) and muTPCT (muTPC Merkle tree). The proposed protocol makes an improvement of tree-based muTESLA. It constructs muTPC to distribute and authenticate the initial parameter of muTESLA. Then it constructs muTPCT to distribute and authenticate the initial parameter of muTPC. Analysis and experiments have shown our proposed protocol has the ability of resisting DoS attacks against the distribution of muTESLA parameters and revoking authenticating powers of compromised nodes on time. It also outperforms the tree-based muTESLA by reducing the cost of computation, communication, and storage needed, which makes our proposed protocol more applicable to large scale sensor networks.