Based on the system theories, this paper discusses the characteristics of complex information system under the strong restraint and strong antagonism conditions and proposes a novel method of constructing complex information system, i. e. multi-living agent method ( MLAM) . Then, the relationship and the difference between the fundamental meaning of MLAM and the existing system theories are studied. Finally, the research scopes of MLAM are outlined and two examples are given to illustrate this method. It is hoped that the proposal of MLAM can help develop a new research field and more people devote to this field.