Abstract: An accurate acoustic localization model has been studied for passive aero-acoustic localization with a small sensor array. Simple model was formed by using three time-delays. An accurate model was obtained by combining all possible simple models with an optimal linear fusion theory. The combination model is more accurate than any simple one. One universal way of modeling the acoustic arrays including spatial array and plane array was created to solve other similar problems. Based on this model, one traditional problem of steering blind region is avoided perfectly for the small array. Taking an example of a small plane square array, this combination model had been tested by means of large amounts of field test data which were TDOA(time difference of arrival) for an acoustic source moves in line, diving, turning and circle trajectory respectively in some heights. Four trajectories were calculated wonderfully. This model is suitable for aero-acoustic source localization with high position accuracy and little variance, particularly for azimuth detection and elevation detection. This way is quite suitable for the widely used plane square array, 4 and 5-elements spatial square array, and standard tetrahedron array.