Abstract: A set of quasi CAV model composed of a external model and a internal model was designed according to foreign public documents,and it was used to study the multi-body interfer-ence during separating by grid force measurement at 0.6m×0.6m transonic/supersonic wind tu-unel.The results show that the aerodynamic characteristcs of the internal model would change dramatically during the separation.While the internal model is leaving the external model along the axis,its aerodynamic characteristcs develops towards the value in free stream.Furthermore, dramatical change of its aerodynamic characteristcs will be induced due to the normal location changing.Two factors induced this dramatic change of the aerodynamic characteristcs.The first comes from the unbalance development of wake flow and the head shock wave during the internal model moving from the wake flow region to free stream flow region,which changes the flow structure of the internal model.And the second comes from the change of local velocity induced by the asymmetric base flow expansion,which induces the more dramatic change of the aerody-namic characteristcs.