The improvement on the shift rules of global and immediate focuses is presented.The improved rules can be used for more extensive domain.Based on Mckeown's focus algorithm,a new algorithm that adopts tree as a controlling structure instead of stack is proposed.It can control the shift of both global and immediate focuses simultaneously.The new algorithm improves the ATN representation of Schema by adding repeat property and priority information to the edge and incorporates the control of the recursion of Schema and backtrack mechanism.The filling and recursion of Schema are determined by the knowledge base.Moreover,the new algorithm can also handle the interchangeable symbols in the Schema.The design of an experimental system based on the proposed algorithm is introduced and the effectiveness of the algorithm is discussed.