Abstract: The efficacy coefficient method was applied to determine the preferred structural plane of rock for the first time.The method had been used to evaluate and forecast the business affairs before.A new method was presented to determine the preferred structural plane of rock and the methods used before were summarized.The shortcomings of traditional methods were removed in this method,i.e.,only the quantity predominance was considered but the quality predominance was ignored,and then the rock structural plane could be evaluated more rationally.After six groups of predominant indexes were summarized to evaluate the structural plane and the satisfactory,and the unallowable indexes of improved efficacy coefficient method were discussed.