Abstract: This paper discusses the relation between a control strategy and inferential efficiency, analyses simply three typical forward-backward mixed control strategies,and reports an one-step forward and all-step backward mixed control strategy that author puts forward in building areogeophysical prospecting expert system. This strategy can make the selection of goals focus the effective goals as fast as possible,can collect neccessary information at any time, and can adapt two modes for exact and inexact reasonings. Therefore, it can both ensure the inferential effect and improve the inferential efficiency. This control strategy has been used in areogeophysical prospecting expert system. The result is satisfactory.