With the rapid development of the Internet of Things (IoT), a huge number of embedded devices are widely used in modern life. Security and privacy have become an important challenge in IoT. Interconnected devices in IoT constitute swarm network. The state trust of swarm devices, or swarm attestation is the key issue for the security of IoT. Traditional remote attestation schemes mainly concentrates on single prover scenario and are lack of large-scale device swarm attestation technology. Targeting at the low efficiency and vulnerability to collusion attack in existing device swarm attestation, in this study, we propose an efficient swarm attestation scheme based on devices grouping. This scheme groups homogeneous devices and sets up a management node in each group to verify the rest of nodes in the same group. When the swarm executing the swarm attestation scheme, the remote verifier only need to verify the management node, because each management node has known its own group's trust state. By this way, this scheme improve the efficiency. It also has high security and is able to resist collusion attack. The prototype system experiment results show that the more homogeneous devices and the less management nodes, the efficiency of the proposed scheme is higher.