Abstract: Coordination is the bottle-neck of system efficiency in multi agent systems. At present, the mechanisms of coordination which are often used are group structure, exchange meta information, multi agent plan, collective goals etc, but collective goals possess the character of the lowest coordination cost. Since collective goals can’t be described with norm logic, it is feasible to present the formal norm of collective goals in some restriction. In this paper, semantics of dynamic probable world is first presented and it is proved on this basis that the conditions of collective goals presented by Sandu are too broad and the unsettled problem is solved: how collective remembers believe each other and realize collective goals at the same time.