Abstract: In order to predict the free-field aircraft engine noise accurately in static engine experiments, the ground reflection effect is analyzed with different ground acoustic impedance models and sound coherence models. Comparison between the experiment data and the prediction results shows that the ground acoustic impedance model is the important factor affecting the ground reflection effect of the noise. The characteristic equation of ground acoustic impedance with fewer factors can be selected to get more accurate prediction results of ground reflection, when there is some uncertainty of the effective ground acoustic impedance. According to the comparison results, a calculation method of ground reflection effect of aircraft engine noise is proposed in this paper, which provides an optimization idea for upgrading engine noise airworthiness prediction program.