Abstract: Using the Maximum Likelihood Estimation method can avoid severe errors of aero-dynamic coefficients as a result of direct differentiating the measured data in wind tunnel free-flight test.This paper introduces the rationale and methodology of the aerodynamic parameter i-dentification technology in the wind tunnel free-flight test in detail.Simulation and test examples are presented.The identification results indicate that the aerodynamic parameter identification from wind tunnel free-flight test data is an effective method in study of aerodynamic characteris-tics of aircrafts.Although force derivatives are hard to identify,moment derivatives are easy to i-dentify and the identification results are close to the engineering results.Meanwhile,the increase of the number of sample points,the improvement of precision of measurements,the installation of overload measuring equipment and the improvement of machining level of test models are all favorable for enhancing the reliabilities of results.