Abstract: Compared with conventional aircrafts,joined/tandem wing aircrafts' induced drags are halved theoretically,whose structure efficiencies are higher and the maximal wing geometry sizes are smaller.Because of the aerodynamic interferences between the frontal wing and the back one,the real aerodynamic efficiency can't reach the theory value and so does the real focus of the aircraft.In this paper,response surface method is adopted to fit the wind tunnel experiment discrete measure data,the amendatory focus of the aircraft is obtained through the principle of composition of forces,the feasibility of the study has been validated through the applications on four kinds of joined/tandem wing free-flight models outfield performances.