Through-flow nacelle (TFN) is an effective method of simulating engine effect in wind tunnel Testing.By adjusting the nozzle exit areas of a TFN, the flow passing the TFN could be controlled and the flow ratio (MFR)could be achieved to make sure the similarity around the inlet flow field.As stall characteristics is one of the important factor in defining civil aircraft performance, a great portion of the low speed wind tunnel tests is devoted to thestudy of the stall characteristics of aircraft in landing configuration; and due to the fact that engines tend to be set atan idle condition during airworthy flight tests for stall speed determination, designing a TFN with a MFR corresponding to an idle power setting is desirable for the prediction of stall characteristics in wind tunnel testing. When running at idle conditions, an engine will have a very low fan pressure ratio, which means if the fan nozzle geometryis maintained, TFN can also be used to simulate approximately the jet effects of idle power setting.A engine running idly will have a MFR of around 0.5, which can be achieved on a TFN which is designed such that the totalnozzle area is half of the highlight area. CFD calculation has proved the effectiveness of this methodology.