In a high bypass ratio aircraft engine, the high-pressure and low-pressure turbines are connected by an intermediate turbine duct (ITD). The aerodynamic performance of the ITD is affected by the incoming flow from the high-pressure turbine. This paper investigates the effects of an incoming wake or/and a near casing streamwise vortex on the flow field and loss of an ITD. For the case with only an incoming wake, the wake interacts with the boundary layer (BL), forming a pair of vortices and causing additional loss. With an incoming streamwise vortex, the casing boundary layer interacts with it and a loss core forms near the casing. When both a wake and a streamwise vortex are present at the inlet, apart from interacting with the boundary layer, the wake and the streamwise vortex could interact with each other. It is found that the distance between the wake and streamwise vortex has a major effect on the flow pattern and aerodynamic loss of ITD. Three different distances between the wake and the incoming streamwise vortex are investigated. When the distance between the wake and incoming streamwise vortex is large, the two flow structures develop relatively independently and the combined effect is small. As the distance between them reduces, the flow structure induced by the wake interacts with the incoming streamwise vortex and suppresses the loss production. However, for the case with the shortest distance, the interaction enhances the loss generation. A simplified analytical model is proposed to explain this loss mechanism.