Mobile Ad hoc NETwork (MANET) is a part of the Intet of Things (IoT).In battlefield communicatinn systems,ground soldiers,tanks,and unmanned aerial vehicles comprise a heterogeneous MANET.In 2006,Byun et al.proposed the first constant-round password-based group key exchange with different passwords for such networks,In 2008,Nam et al.discovered the shortcomings of the scheme,and modified it.But the works only provide the group key,In this paper,we propose a password-based secure communication scheme for the IoT,which could be applied in the battlefield communication systems and support dynamic group,in which the nodes join or leave.By performing the scheme,the nodes in the heterogeneous MANET can realize secure broadcast,secure tmicast,and secure direct communication across realms.After the analyses,we demonstrate that the scheme is secure and efficient.