Identity-based multi-recipient signcryption (IDMRSC) is an extension of identity-based signcryttion. At first, a new IDMRSC algorithm is proposed based on bilinear pairings and its security and efficiency are analyzed. The result shows that the algorithm is provable secure in the random oracle model. Furthermore, the algorithm is significantly efficient and of low computation cost and communication overhead, and is very suitable for secure communication in Ad hoc networks. Finally, the method of using IDMRSC algorithm to deal with malicious nodes in Ad hoc networks is expounded. This IDMRSC algorithm can meet the high level secure requirement in practical application and therefore, is of a certain practical value in application.