First, the recent research on complex system and complexity from both China and abroad are briefly described in this paper. Then macro economy decision making is discussed. Macro economy decision making belongs to the category of open complex giant system. One effective method for solving this problem is the hall for workshop of metasynthetic engineering proposed by professor Qian Xue sen in 1992. Combined with qualitative comprehension of expert group and processed with appropriate methods of modeling, it can resolve the complex problem at last．The hall for workshop is composed of three paft ：expert group system，information and knowledge system，computer technology of hardware＆ software．Since expert group plays an extrod inary important role in the hall for workshop，and both expert’s individual behavior and group behavior have a direct effect on the decision making．The thought and behavior of expert’s individual and group are inevitably imperfect．Their behavior is under the control of be havioral rule of the individual and group．In this paper，based on the analysis of faults in individual be havior and group behavior，a behavior norm is establlshed for experts in the hall to help them to overcome their defeets-With advanced decision making technology and instruments and modeling methodology，better decision making can be expected．