Abstract: Based on a new possible worlds semantic and Rao ＆ Georgeff’s BDI formalization which based on a branching time possible worlds model, an improved BDI model is given in this paper. Comparing with Rao ＆ Georgeff’s BDI model and most possible worlds formalisms, in this improved BDI model there are not the logical omniscience problem and the side effect problems except in case of equivalence.